JP2013012691A - Method for manufacturing thin film solar cell and thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a thin film solar cell, capable of improving light utilization efficiency thereof, and a thin film solar cell.SOLUTION: A method for manufacturing a thin film solar cell including a plurality of photoelectric conversion layers comprises the steps of: forming a surface transparent electrode 12 on a transparent substrate 11; forming a first texture 12a with a first cycle, for scattering light in the absorption wavelength region of a top cell 13, on the surface transparent electrode 12; forming the top cell 13 and a bottom cell 14 on the surface transparent electrode 12; forming a translucent conductive oxide layer 16 on the bottom cell 14; and forming a second texture 16a with a second cycle, for scattering light in the absorption wavelength region of the bottom cell 14, on the translucent conductive oxide layer 16.

Description

  The present invention relates to a method for manufacturing a thin film solar cell and a thin film solar cell.

  Conventionally, a tandem-type thin film solar cell having a plurality of photoelectric conversion layers is known (see, for example, Patent Document 1). An example of the configuration of this thin film solar cell is shown in FIG. This thin film solar cell has a structure in which a transparent substrate 101 on which light is incident, a transparent electrode 102, a first photoelectric conversion layer 103, an intermediate layer 104, a second photoelectric conversion layer 105, a buffer layer 106, and a back electrode 107 are laminated in order. Have The first photoelectric conversion layer 103 is formed of amorphous silicon that absorbs light of 700 nm or less. The second photoelectric conversion layer 105 is formed of microcrystalline silicon that absorbs light having a long wavelength of 1100 nm or less, and can absorb light in the infrared region included in sunlight.

  In addition, a so-called texture 102 a having a concavo-convex structure is formed on the surface of the transparent electrode 102 on the back electrode 107 side. The texture 102a scatters the light incident on the thin film solar cell, thereby increasing the substantial optical path length in each of the photoelectric conversion layers 103 and 105 and increasing the amount of absorbed light.

  In such a texture 102a, the wavelength of light that can be scattered is determined by the period (hereinafter referred to as pitch) that is the length from the top of the convex part to the top of the adjacent convex part. That is, it is impossible to scatter light in all the wavelength ranges of sunlight by the texture 102a having one pattern. For this reason, in general, the pitch of the texture 102 a is determined according to the wavelength region on the short wavelength side absorbed by the first photoelectric conversion layer 103. Therefore, with this texture 102a alone, light on the long wavelength side such as the infrared region cannot be scattered, and light loss has occurred.

  Therefore, as shown in FIG. 9, a thin film solar cell in which a first texture 112a having a long pitch is formed on a transparent electrode 112 on a transparent substrate 111 and a second texture 112b having a short pitch is formed on the surface is proposed. Has been. In this configuration, light having a wavelength that is easily absorbed by the first photoelectric conversion layer 103 and light having a wavelength that is easily absorbed by the second photoelectric conversion layer 105 can be scattered.

International Publication No. 2010/032490

  The transparent electrode 112 having the above two textures 112a and 112b is often formed of a conductive oxide film (hereinafter referred to as a conductive oxide film) such as indium tin oxide (ITO). Although this conductive oxide film is translucent, it has a lower light transmittance than, for example, a transparent substrate. When a texture with a long pitch such as the first texture 112a is formed on the conductive oxide film, the conductive oxide film must be thickened by that amount, and each photoelectric conversion layer 103 is interposed via the transparent electrode 112. , 105 side is reduced in light quantity. That is, in the thin film solar cell, the amount of light transmitted to the photoelectric conversion layers 103 and 105 is reduced even if the range of wavelengths that can be scattered within the battery cell is expanded. It is difficult to improve the light utilization efficiency.

  Such problems are not limited to thin film solar cells having two photoelectric conversion layers having different maximum wavelength regions, and transparent electrodes as described above are employed even for thin film solar cells having a single photoelectric conversion layer. In such a case, it occurs in common.

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

  In order to solve the above-mentioned problems, the invention according to claim 1 is a method of manufacturing a thin film solar cell including a plurality of photoelectric conversion layers, a step of forming a surface transparent electrode on a transparent substrate, and the surface transparent electrode. A step of forming an uneven structure having a first period that scatters light in an absorption wavelength region of the first photoelectric conversion layer among the photoelectric conversion layers, and the photoelectric conversion layers on the surface transparent electrode. A step of forming, a step of forming a translucent conductive oxide layer on the photoelectric conversion layer, and an absorption of a second photoelectric conversion layer among the photoelectric conversion layers in the translucent conductive oxide layer. And a step of forming a concavo-convex structure having a second period that scatters light in a wavelength region.

  According to the first aspect of the present invention, in order to increase the light utilization efficiency, the uneven structure that scatters light in the absorption wavelength region of the first photoelectric conversion layer and the absorption wavelength region of the second photoelectric conversion layer. A step of forming an uneven structure for scattering light was provided. At that time, those concavo-convex structures were formed at different positions. That is, since both of the concavo-convex structures are not formed on the surface transparent electrode, it is not necessary to increase the thickness of the surface transparent electrode in order to secure a space for both of the concavo-convex structures. For this reason, even when forming such an uneven structure to improve the light utilization efficiency, a battery structure that does not reduce the amount of light transmitted to the photoelectric conversion layer side can be obtained. The effect of improving the light utilization efficiency can be sufficiently exhibited.

  According to a second aspect of the present invention, in the method of manufacturing a thin film solar cell according to the first aspect, the step of forming the concavo-convex structure having the second period on the translucent conductive oxide layer includes the translucency. The gist is to form a thin film in which constituent particles are arranged along the second period on the conductive oxide layer, and wet-etch the light-transmitting conductive oxide layer on which the thin film is formed.

  According to the invention described in claim 2, in order to wet-etch the translucent conductive oxide through the thin film in which the constituent particles are arranged along the second period, a convex portion is provided at the position of each constituent particle. Or the recessed part provided between this convex part can be formed in a 2nd period. For this reason, it is possible to form a concavo-convex structure with good dimensional accuracy in a short time as compared with the case of performing wet etching without using a thin film.

  According to a third aspect of the present invention, in the method for manufacturing a thin-film solar cell according to the second aspect, a metal is formed on a surface of the translucent conductive oxide layer on which the concavo-convex structure of the second period is formed. The method further comprises the step of forming a reflective layer comprising: the thin film is made of the same material as the reflective layer, or a metal having a light reflectance equal to or higher than the light reflectance of the reflective layer.

  According to the invention described in claim 3, since the thin film is made of the same material as the reflective layer or a metal having a light reflectance equal to or higher than the light reflectance of the reflective layer, the constituent particles of the thin film remain in the concavo-convex structure. Even if a reflective layer is formed on the constituent particles, the light reflectance of the reflective layer can be suppressed from decreasing.

  Invention of Claim 4 is a manufacturing method of the thin film solar cell of any one of Claims 1-3, The uneven | corrugated structure of a said 2nd period is the translucent conductive oxide layer. The gist is that it is formed on the surface in contact with the second photoelectric conversion layer.

  According to the fourth aspect of the present invention, the concave-convex structure having the second period that scatters the light in the absorption wavelength region of the second photoelectric conversion layer is formed on the surface in contact with the second photoelectric conversion layer. Therefore, the light scattered by the uneven structure can be easily absorbed by the second photoelectric conversion layer.

  The invention according to claim 5 is formed on the transparent substrate, the surface transparent electrode formed on the transparent substrate, the plurality of photoelectric conversion layers formed on the surface transparent electrode, and the photoelectric conversion layer. The surface transparent electrode has an uneven structure with a first period that scatters light in the absorption wavelength region of the first photoelectric conversion layer among the photoelectric conversion layers. The light-transmitting conductive oxide layer is formed with an uneven structure having a second period that scatters light in the absorption wavelength region of the second photoelectric conversion layer among the photoelectric conversion layers. And

  According to invention of Claim 5, in order to improve the utilization efficiency of light, the thin film solar cell was provided with the uneven structure corresponding to the absorption wavelength range of a some photoelectric converting layer, respectively. At that time, the concavo-convex structure that scatters light in the absorption wavelength region of the first photoelectric conversion layer and the concavo-convex structure that scatters light in the absorption wavelength region of the second photoelectric conversion layer were formed at different positions. That is, since both of these concavo-convex structures are not formed on the surface transparent electrode, it is not necessary to increase the thickness of the surface transparent electrode in order to secure both spaces of each concavo-convex structure. For this reason, even when forming such an uneven structure to improve the light utilization efficiency, a battery structure that does not reduce the amount of light transmitted to the photoelectric conversion layer side can be obtained. The effect of improving the light utilization efficiency can be sufficiently exhibited.

Sectional drawing of the thin film photovoltaic cell of 1st Embodiment which actualized the thin film photovoltaic cell of this invention. It is sectional drawing explaining the manufacturing process of the cell, (a) is a process of laminating a surface transparent electrode, (b) is a process of forming the 1st texture in the electrode, (c) is forming a photoelectric conversion layer. The process to perform is shown. It is sectional drawing explaining the manufacturing process of the cell, Comprising: (a) shows the process of laminating | stacking a translucent conductive oxide layer, (b) shows the process of forming a 2nd texture. It is sectional drawing explaining the manufacturing process of the cell, Comprising: The process of laminating | stacking a metal layer on a translucent conductive oxide layer is shown. It is sectional drawing explaining the manufacturing process of the thin film photovoltaic cell of 2nd Embodiment which actualized the thin film solar cell of this invention, (a) is the process of forming a thin film in a translucent conductive oxide layer, b) is an enlarged view of the main part. It is sectional drawing explaining the manufacturing process, Comprising: (a) is sectional drawing of the translucent conductive oxide layer in which the 2nd texture was formed, (b) is the principal part enlarged view. It is sectional drawing explaining the manufacturing process of the thin film photovoltaic cell of 3rd Embodiment which actualized the thin film solar cell of this invention, Comprising: (a) is a translucent conductive oxide layer in which the 2nd texture was formed. Sectional drawing and (b) are the principal part enlarged views. Sectional drawing of the conventional thin film solar cell. Sectional drawing of the conventional transparent electrode.

(First embodiment)
Hereinafter, the manufacturing method of the thin film solar cell of this invention and 1st Embodiment which actualized the thin film solar cell are demonstrated with reference to FIGS.

  First, the structure and operation of the thin film solar cell of this embodiment will be described with reference to FIG. A thin film solar battery cell 10 shown in FIG. 1 is one cell constituting a thin film solar battery. The thin film solar cell is modularized with the cells connected in series and integrated.

  The thin film photovoltaic cell 10 includes a transparent substrate 11 on the incident surface of sunlight. On the transparent substrate 11, a front transparent electrode 12, a photoelectric conversion layer 15, a back electrode 18, and a protective layer 19 are sequentially laminated in the light incident direction (the arrow direction indicated by a two-dot chain line in the figure). In FIG. 1, the thickness ratio of each layer does not necessarily match the actual thickness ratio.

  The transparent substrate 11 is formed from an insulating material such as various types of glass or transparent resin. The surface transparent electrode 12 is formed from a thin film of a transparent conductive oxide (TCO). Examples of the translucent conductive oxide used for the surface transparent electrode 12 include aluminum-containing zinc oxide (AZO), gallium-containing zinc oxide (GZO), indium tin oxide (ITO), and fluorine-containing tin oxide (FTO). .

  Of each surface of the surface transparent electrode 12, a concavo-convex structure having a plurality of convex portions, that is, a first texture 12a is formed on the surface on the photoelectric conversion layer 15 side in order to increase the utilization efficiency of incident light. The convex portion has a substantially pyramid or conical shape, and the length from the top of the convex portion to the top of another convex portion adjacent to the convex portion (hereinafter referred to as the first pitch (period)) is , Approximately in the range of 100 nm to 150 nm (1000 to 1500 mm).

The photoelectric conversion layer 15 includes a top cell 13 that is a first photoelectric conversion layer and a bottom cell 14 that is a second photoelectric conversion layer.
The top cell 13 is made of amorphous silicon, and sequentially from the light incident side (transparent substrate 11 side), a p-type semiconductor layer to which a p-type impurity is added, an i-type semiconductor layer to which no impurity is added, and an n-type impurity. Has a structure in which n-type semiconductor layers to which is added are stacked (not shown). The top cell 13 absorbs light in a wavelength region (first wavelength region) of 700 nm or less.

  The bottom cell 14 is made of a microcrystalline silicon thin film, and in order from the light incident side (transparent substrate 11 side), a p-type semiconductor layer to which a p-type impurity is added, an i-type semiconductor layer to which no impurity is added, and n It has a structure in which n-type semiconductor layers doped with type impurities are stacked (not shown). This bottom cell 14 absorbs light in a wavelength region (second wavelength region) of 1100 nm or less.

  Since the top texture 13 has the first texture 12a formed on the surface transparent electrode 12 serving as a base, the top cell 13 extends along the first texture 12a on the surface on the surface transparent electrode 12 side and the surface on the opposite side. It has an uneven structure with a first pitch. Further, each surface of the p-type semiconductor layer, the i-type semiconductor layer, and the n-type semiconductor layer also has an uneven structure with a first pitch. Further, since the bottom cell 14 has the first pitch uneven structure formed on the top cell 13 serving as a base, the first pitch uneven structure is formed on the surface on the top cell 13 side and the opposite surface. Have. In addition, each surface of the p-type semiconductor layer, i-type semiconductor layer, and n-type semiconductor layer of the bottom cell 14 has an uneven structure with a first pitch.

  The back electrode 18 has a two-layer structure of a translucent conductive oxide layer 16 as a translucent conductive oxide layer that functions as a transparent electrode and a metal layer 17 that functions as a reflective layer. Similar to the surface transparent electrode 12, the translucent conductive oxide layer 16 is made of aluminum-containing zinc oxide (AZO), gallium-containing zinc oxide (GZO), indium tin oxide (ITO), fluorine-containing tin oxide (FTO), or the like. It is comprised from a translucent conductive oxide. The metal layer 17 is made of a material having a high light reflectance such as silver, aluminum, or copper.

  The translucent conductive oxide layer 16 has an uneven structure with a first pitch along the contact surface of the bottom cell 14 on the contact surface with the bottom cell 14. Further, the translucent conductive oxide layer 16 has a concavo-convex structure formed at a pitch larger than the first pitch, that is, a second texture 16 a on the contact surface with the metal layer 17. The convex portion of the second texture 16a also has a substantially pyramid or conical shape, and the length from the top of the convex portion to the top of another convex portion adjacent to the convex portion (hereinafter referred to as the second pitch). (Period)) is approximately in the range of 0.5 μm to 2 μm.

  Further, the metal layer 17 has a second pitch along the second texture 16a of the translucent conductive oxide layer 16 on the contact surface with the translucent conductive oxide layer 16 and the surface on the opposite side. Has an uneven structure.

  Further, the protective layer 19 is made of a material having a barrier property against moisture or the like, such as titanium, titanium oxide, nickel-vanadium alloy. Of the protective layer 19, the contact surface with the metal layer 17 and the opposite surface have a concavo-convex structure with a second pitch along the concavo-convex structure of the metal layer 17 serving as a base.

  Next, operation | movement of this thin film photovoltaic cell 10 is demonstrated. Sunlight incident from the transparent substrate 11 side enters the surface transparent electrode 12. At that time, part of the light in the first wavelength region that can be absorbed by the top cell 13 is refracted by the first texture 12 a of the surface transparent electrode 12. As a result, the optical path length becomes longer than when the light is incident perpendicularly to the surface of the photoelectric conversion layer 15, and the light is easily absorbed by the top cell 13. Further, another part of the light in the first wavelength band is reflected on the side surface of the convex portion or the concave portion of the first texture 12a to change the traveling direction, and is incident again on the side surface of the other convex portion or the concave portion. A part of the incident light passes through the surface transparent electrode 12 and enters the photoelectric conversion layer 15.

  Further, in the photoelectric conversion layer 15, the first pitch uneven structure formed on the contact surface with the back electrode 18 and the p layer, i layer, and n layer in the photoelectric conversion layer 15 is also in the first wavelength region. The light once refracted or once reflected by the convex portion is re-entered into the photoelectric conversion layer 15. Therefore, by forming the first texture 12a, the amount of light that is reflected and not absorbed by the interface between the surface transparent electrode 12 and the photoelectric conversion layer 15 is reduced, and the first wavelength into the photoelectric conversion layer 15 is reduced. The confinement effect of the region is improved, and the light absorption rate can be increased.

  In addition, a part of the light in the second wavelength region that has reached the translucent conductive oxide layer 16 without being absorbed by the bottom cell 14 is reflected by the side surfaces of the convex portion or the concave portion constituting the second texture 16a. Re-enters the conversion layer 15. Further, the light transmitted through the translucent conductive oxide layer 16 is reflected at the interface with the metal layer 17. Therefore, the confinement effect of light in the second wavelength region in the photoelectric conversion layer 15 is improved, and the light absorption rate can be increased. Further, since the thin-film solar battery 10 has a structure in which the bottom cell 14 and the back electrode 18 on which the second texture 16a is formed are adjacent to each other, the light in the second wavelength region reflected by the second texture 16a or the like is reflected. , And is easily absorbed by the bottom cell 14.

  Next, the manufacturing method of the thin film solar cell in this embodiment is demonstrated with reference to FIGS. In the process of manufacturing the thin-film solar battery 10, the surface transparent electrode 12, the photoelectric conversion layer 15, the back electrode 18 and the protective layer 19 are sequentially laminated on the transparent substrate 11. Moreover, when manufacturing an integrated-type thin film solar cell, after each layer is formed into a film as needed, the patterning which divides | segments for every cell with laser beams, such as YAG, shall be performed.

  First, as shown in FIG. 2A, the surface transparent electrode 12 is formed on one surface of the transparent substrate 11. The transparent substrate 11 serving as the base can be formed of various glass substrates such as soda lime silicate glass, aluminosilicate glass, borate glass, lithium aluminosilicate glass, and quartz glass. Or the transparent substrate 11 can also be formed with various translucent resin, such as a polyethylene terephthalate (PET), a polyimide, a polycarbonate, and an acryl.

When the surface transparent electrode 12 is formed, a target of a conductive oxide as a material is sputtered by plasma generated from an inert gas such as argon.
Next, a process of forming the first texture 12a is performed on the surface transparent electrode 12. In the present embodiment, wet etching is performed using an etching solution such as a mixed solution of fluorine-based hydrochloric acid, sulfuric acid, and nitric acid such as ammonium hydrogen fluoride, ammonium fluoride, and a mixture thereof. First, the precursor of the thin-film solar battery cell 10 having the surface transparent electrode 12 as the uppermost layer is placed on a belt that travels in a liquid tank filled with an etching solution and is conveyed in the liquid tank. And if the said precursor is taken out from a liquid tank, the washing | cleaning process wash | cleaned with water etc. and the drying process will be performed. As a result, as shown in FIG. 2B, the first texture 12 a having the first pitch is formed on the surface of the surface transparent electrode 12.

Next, the top cell 13 made of amorphous silicon is formed in the order of the p layer, the i layer, and the n layer by plasma CVD. At this time, monosilane (SiH ₄ ) gas, hydrogen gas (H ₂ ), and diborane gas (B ₂ H ₆ ) are used as raw material gases, and plasma of the raw material gas is generated in the vacuum chamber so that radical species such as SiH ₃ are generated. Generate. Then, a p-type semiconductor layer made of amorphous silicon to which boron is added is formed on the surface transparent electrode 12. Next, using, for example, monosilane gas as a source gas, an i-type semiconductor layer made of amorphous silicon to which no impurity is added is formed on the p-type semiconductor layer. Further, an n-type semiconductor layer made of amorphous silicon to which phosphorus is added is formed using, for example, monosilane gas, hydrogen gas, and phosphine (PH ₃ ) as a source gas.

Next, the bottom cell 14 made of microcrystalline silicon is formed in the order of the p layer, the i layer, and the n layer by plasma CVD. At this time, the same raw material gas as that for forming each layer of the top cell 13 is used. For example, the flow rate ratio of hydrogen gas in the raw material gas is relatively increased. When the ratio of hydrogen gas in the source gas increases, the ratio of hydrogen atoms to SiH ₃ radicals increases in the plasma, and microcrystalline silicon in which amorphous and crystals are mixed easily grows.

  As a result, as shown in FIG. 2C, the top cell 13 and the bottom cell 14 are sequentially laminated on the surface transparent electrode 12. As described above, since the top cell 13 and the bottom cell 14 are based on the surface transparent electrode 12, the contact surface with the surface transparent electrode 12, the top surface of the bottom cell 14, the p layer, the i layer, and the n layer. Each surface has a concavo-convex structure along the first texture 12a.

  Next, the translucent conductive oxide layer 16 is formed on the photoelectric conversion layer 15. At this time, the target of the conductive oxide is sputtered by plasma generated from an inert gas such as argon. For example, when forming the translucent conductive oxide layer 16 made of AZO, the target is, for example, zinc oxide to which aluminum is added at a ratio of 0.1 wt% to 10 wt%.

  As described above, in the state where the light-transmitting conductive oxide layer 16 is simply formed on the photoelectric conversion layer 15, the photoelectric conversion layer 15 is included in the light-transmitting conductive oxide layer 16 as shown in FIG. And the surface on the opposite side have a concavo-convex structure with a first pitch along the concavo-convex structure of the photoelectric conversion layer 15 serving as a base.

  Next, a step of forming the second texture 16a is performed on the translucent conductive oxide layer 16. In the present embodiment, wet etching is performed using an etching solution such as a mixed solution of fluorine-based hydrochloric acid, sulfuric acid, and nitric acid such as ammonium hydrogen fluoride, ammonium fluoride, and a mixture thereof. The wet etching operation itself is performed in the same manner as the wet etching with the surface transparent electrode 12 as a processing target, but the conditions such as the composition of the etching solution and the time for immersing the precursor in the etching solution are different. As a result, as shown in FIG. 3B, the second texture 16 a having the above-described second pitch is formed on the upper surface of the translucent conductive oxide layer 16.

  Next, as shown in FIG. 4, a metal layer 17 is formed on the translucent conductive oxide layer 16 on which the second texture 16a is formed by various deposition methods such as sputtering. The metal layer 17 formed in this way has a concavo-convex structure with a second pitch along the second texture 16a of the light-transmitting conductive oxide layer 16 as a base.

When the metal layer 17 is formed, a protective layer 19 made of a material such as titanium, titanium oxide, or nickel-vanadium alloy is formed thereon by a sputtering method.
When integrating the thin film solar cells 10, the thin film solar cells 10 are connected in series by a lead frame or the like. Then, the electrically connected thin-film solar cells 10 are sandwiched between each tempered glass, a sealing material such as EVA (ethylene vinyl acetate), a weather-resistant film, and the like to be modularized.

According to the first embodiment, the following effects can be obtained.
(1) In 1st Embodiment, in order to improve the utilization efficiency of light, it was set as the structure provided with the photoelectric converting layer 15 comprised from the top cell 13 and the bottom cell 14 in the thin film solar cell. Furthermore, a first texture 12a that is a first-period uneven structure that scatters light in the absorption wavelength region (first wavelength region) of the top cell 13 is formed on the surface transparent electrode 12 of the thin-film solar cell, and the back electrode A second texture 16 a that scatters light in the absorption wavelength region (second wavelength region) of the bottom cell 14 was formed on the translucent conductive oxide layer 16 that constitutes 18. That is, since both the first texture 12a and the second texture 16a are not formed on the surface transparent electrode 12, but are formed at different positions, the surface transparent electrode 12 is thickened to secure both spaces of each concavo-convex structure. There is no need to do. For this reason, even when the first texture 12a and the second texture 16a are formed in the cell, the amount of light lost by the surface transparent electrode 12 can be reduced. The effect can be fully exhibited.

  (2) In the second embodiment, the second texture 16 a is formed on the surface of the translucent conductive oxide layer 16 that contacts the bottom cell 14. Therefore, the light in the second wavelength range scattered by the second texture 16a can be easily absorbed by the bottom cell 14 having the second wavelength range as the absorption wavelength range.

(Second Embodiment)
Hereinafter, the manufacturing method of the thin film solar cell of this invention and 2nd Embodiment which actualized the thin film solar cell are demonstrated with reference to FIG.3 and FIG.5-6. In addition, since 2nd Embodiment is a structure which only changed the process of forming the 2nd texture 16a among the manufacturing methods of the thin film solar cell of 1st Embodiment, the detailed description is given about the same part. Omitted.

  In the step of forming the second texture 16a, after the translucent conductive oxide layer 16 is laminated on the photoelectric conversion layer 15 (see FIG. 3A), as shown in FIG. A thin film 22 made of a metal such as silver, gold, aluminum, or copper is formed to a thickness of 100 mm or less on the surface of the oxide layer 16 having an uneven structure with a first pitch. When the thin film 22 is formed to the thickness, as shown in FIG. 5B, the constituent particles 22P of the thin film 22 are distributed on the translucent conductive oxide layer 16 with a gap. . At this time, the interval between the constituent particles 22P is approximately the same as the second pitch described above. In FIG. 5A, the concavo-convex structure is greatly illustrated for convenience.

  When the thin film 22 is formed, the precursor of the thin film photovoltaic cell 10 is exposed to an etching solution, and the light-transmitting conductive oxide layer 16 is wet-etched. At this time, the etching solution may be a fluorine-based solution such as ammonium hydrogen fluoride, ammonium fluoride, or a mixed solution thereof, or a mixed solution of hydrochloric acid, sulfuric acid, and nitric acid. The wet etching process is the same as the wet etching process for the light-transmitting conductive oxide layer 16 of the first embodiment, but the composition of the etchant, the time for immersing the precursor in the etchant, etc. The conditions are different.

  As a result, as shown in FIG. 6B, erosion starts from the contact surface between the constituent particles 22P of the thin film 22 and the translucent conductive oxide layer 16, and a crater-shaped recess is formed around the constituent particles 22P. Is done. Thereby, the convex part around the constituent particles 22P is eroded, and the part of the surface of the translucent conductive oxide layer 16 that is not eroded becomes a new convex part. At this time, some of the constituent particles 22P disappear due to erosion. Thus, the phenomenon in which the concave portions are formed around the constituent particles 22P is assumed that the constituent particles 22P exert some catalytic action. Therefore, by performing wet etching in this way, as shown in FIG. 6A, the second texture 16a having a pitch larger than that of the first texture 12a can be obtained in a relatively short time and in a dry etching apparatus or the like. It can be formed without using an expensive apparatus. When the wet etching is completed in this way, a cleaning process using water or the like and a drying process are performed.

  Further, a metal layer 17 made of silver, aluminum, and copper is formed on the precursor, and the material constituting the thin film 22 and the material of the metal layer 17 are the same. Alternatively, the material constituting the thin film 22 is a material having a higher light reflectance than the material constituting the metal layer 17. For example, when the metal layer 17 is made of aluminum, the thin film 22 is made of silver. In this way, even if the constituent particles 22P of the thin film 22 remain in the translucent conductive oxide layer 16 when the metal layer 17 is formed, the light reflectance of the metal layer 17 is adversely affected. Can not be.

Therefore, according to the second embodiment, the following effects can be obtained in addition to the effects described in the first embodiment.
(3) In the second embodiment, in the step of forming the second texture 16a on the translucent conductive oxide layer 16, the constituent particles 22P are arranged in the translucent conductive oxide layer 16 along the second pitch. A thin film 22 was formed, and the light-transmitting conductive oxide layer 16 on which the thin film 22 was formed was wet etched. Thereby, the crater-like recessed part provided between convex parts can be formed in the position of each constituent particle 22P, and the uneven structure along the 2nd pitch can be formed. Therefore, it is possible to form the second texture 16a with high dimensional accuracy in a short time as compared with the case where the wet etching is performed without using the thin film 22.

  (4) In 2nd Embodiment, the thin film 22 for forming the 2nd texture 16a among the translucent conductive oxide layers 16 is the same material as the metal layer 17, or more than the light reflectivity of the metal layer 17. It was formed from a metal having a light reflectance of For this reason, even if the constituent particles 22P of the thin film 22 remain on the surface on which the second texture 16a is formed and the metal layer 17 is formed on the constituent particles 22P, the light reflectance of the metal layer 17 is reduced. Can be suppressed.

(Third embodiment)
Hereinafter, the manufacturing method of the thin film solar cell and the third embodiment in which the thin film solar cell is embodied will be described with reference to FIGS. 3, 5, and 7. In addition, since 3rd Embodiment is a structure which only changed the process of forming the 2nd texture 16a among the manufacturing methods of the thin film solar cell of 1st Embodiment, the detailed description is given about the same part. Omitted.

  In the step of forming the second texture 16a, after forming the translucent conductive oxide layer 16 on the photoelectric conversion layer 15 (see FIG. 3A), the first pitch is formed as shown in FIG. 5A. A thin film 22 made of a metal such as silver, aluminum, or copper, or an oxide such as silicon dioxide or titanium dioxide is formed on the surface having the concavo-convex structure having a thickness of 100 mm or less. When the thin film 22 is formed to the thickness, as shown in FIG. 5B, the constituent particles 22P of the thin film 22 are distributed on the translucent conductive oxide layer 16 with a gap. . At this time, the interval between the constituent particles 22P is approximately the same as the second pitch described above.

  When the thin film 22 is formed, the precursor of the thin film photovoltaic cell 10 is exposed to an etching solution, and the light-transmitting conductive oxide layer 16 is wet-etched. At this time, the etching solution may be a fluorine-based solution such as ammonium hydrogen fluoride, ammonium fluoride, or a mixed solution thereof, or a mixed solution of hydrochloric acid, sulfuric acid, and nitric acid. The wet etching process is the same as the wet etching process for the surface transparent electrode 12 of the first embodiment, but the etching solution composition and the time for immersing the precursor in the etching solution are approximately 45 seconds. ~ 90 seconds.

  As a result, as shown in FIG. 7A, the constituent particles 22P of the thin film 22 function as a mask for the translucent conductive oxide layer 16, and the exposed regions not covered by the constituent particles 22P are eroded. Accordingly, as shown in FIG. 7B, the convex portions around the constituent particles 22P are eroded, and the second texture 16a having a pitch larger than that of the first texture 12a is formed.

  When the thin film 22 is not formed of the same material as the metal layer 17, or is formed of a material having a light reflectance higher than that of the metal layer 17, the translucent conductive oxide layer In order to remove the constituent particles 22P from 16, a cleaning process using nitric acid or the like is performed. Thereafter, a washing step with water or the like and a drying step are performed. Further, when the thin film 22 is formed of the same material as that of the metal layer 17, or when it is formed of a material having a light reflectance equal to or higher than that of the metal layer 17, a cleaning process using water or the like and drying are performed. Perform the process.

And the metal layer 17 is formed into a film with respect to the translucent conductive oxide layer 16 in which the 2nd texture 16a was formed by sputtering method.
Therefore, according to the third embodiment, the following effects can be obtained in addition to the effects described in the first embodiment.

  (5) In the third embodiment, in the step of forming the second texture 16a in the translucent conductive oxide layer 16, the constituent particles 22P are arranged in the translucent conductive oxide layer 16 along the second pitch. A thin film 22 was formed, and the light-transmitting conductive oxide layer 16 on which the thin film 22 was formed was wet etched. For this reason, each constituent particle 22P functions as a mask, a portion not covered with the constituent particle 22P is etched, a new convex portion is formed at the position of the constituent particle 22P, and a concavo-convex structure along the second pitch is formed. Can be formed. For this reason, it is possible to form the second texture 16a with good dimensional accuracy in a short time as compared with the case where the wet etching is performed without using the thin film 22.

  (6) In 2nd Embodiment, the thin film 22 for forming the 2nd texture 16a among the translucent conductive oxide layers 16 is the same material as the metal layer 17, or more than the light reflectivity of the metal layer 17. It was formed from a metal having a light reflectance of For this reason, even if the constituent particles 22P of the thin film 22 remain in the concavo-convex structure and the metal layer 17 is formed on the constituent particles 22P, the light reflectance of the metal layer 17 can be suppressed from decreasing.

In addition, you may change each said embodiment as follows.
In the first embodiment, the wet etching method is used in the step of forming the first texture 12a and the second texture 16a. However, a fluorine-based gas, a chlorine-based gas, an oxygen-containing gas, or a carbon-containing gas is used. An etching reaction and a deposition reaction may be generated by a combined dry etching method. Further, the concavo-convex structure may be formed by laser, or the concavo-convex structure may be mechanically formed by nanoimprint or the like.

  ・ In each wet etching process, ultrasonic waves are propagated in the etching solution in which the precursor is immersed, bubbles are generated in the etching solution in which the precursor is immersed, or the etching solution is dropped on the precursor in a spray form. Thus, the concavo-convex structure may be formed.

  In each of the above embodiments, the thin-film solar battery 10 is of a type that includes the transparent substrate 11 on the sunlight incident surface. However, the transparent substrate 11 is omitted, and the transparent conductive oxide is disposed on the sunlight incident surface. You may make it a type provided with a layer.

The thin film solar cell 10 may have a structure in which an intermediate layer is interposed between the first photoelectric conversion layer 103 and the second photoelectric conversion layer 105.
In each of the above embodiments, the second texture 16a is formed on the translucent conductive oxide layer 16, but other positions such as being formed on the surface of the bottom cell 14 on the translucent conductive oxide layer 16 side. You may make it form in.

  In each of the above embodiments, the thin-film solar cell 10 has a structure in which the light-transmitting conductive oxide layer 16 is laminated with the metal layer 17 and the protective layer 19, but the light-transmitting conductive oxide layer 16 has It is good also as a structure which laminated | stacked the white sheet | seat which consists of EVA (ethylene vinyl acetate) which has reflectivity.

  In each of the above embodiments, the thin-film solar battery of the present invention is embodied as a two-junction type battery, but the photoelectric conversion layer 15 may be composed of three or more layers, such as a three-junction type including a middle cell.

  DESCRIPTION OF SYMBOLS 11 ... Transparent substrate, 12 ... Surface transparent electrode, 13 ... Top cell which comprises 1st photoelectric converting layer, 14 ... Bottom cell which comprises 2nd photoelectric converting layer, 15 ... Photoelectric converting layer, 16 ... Translucent conductivity Oxide layer, 12a: first texture as first-period concavo-convex structure, 16a: second texture as second-period concavo-convex structure, 22: thin film, 22P: constituent particles.

Claims (5)

In the method for manufacturing a thin-film solar cell including a plurality of photoelectric conversion layers,
Forming a surface transparent electrode on a transparent substrate;
Forming a concavo-convex structure of a first period that scatters light in the absorption wavelength region of the first photoelectric conversion layer among the photoelectric conversion layers in the surface transparent electrode;
Forming each of the photoelectric conversion layers on the surface transparent electrode;
Forming a light-transmitting conductive oxide layer on the photoelectric conversion layer;
Forming an uneven structure having a second period for scattering light in the absorption wavelength region of the second photoelectric conversion layer among the photoelectric conversion layers in the light-transmitting conductive oxide layer. A method for manufacturing a thin film solar cell. The step of forming the concavo-convex structure of the second period in the translucent conductive oxide layer includes:
The thin film in which constituent particles are arranged along the second period is formed on the transparent conductive oxide layer, and the transparent conductive oxide layer on which the thin film is formed is wet-etched. The manufacturing method of the thin film solar cell of description. A step of forming a reflective layer made of metal on the surface of the translucent conductive oxide layer on which the concavo-convex structure of the second period is formed;
The method of manufacturing a thin film solar cell according to claim 2, wherein the thin film is made of the same material as the reflective layer, or a metal having a light reflectance equal to or higher than the light reflectance of the reflective layer.   4. The thin film according to claim 1, wherein the concavo-convex structure of the second period is formed on a surface of the translucent conductive oxide layer that is in contact with the second photoelectric conversion layer. A method for manufacturing a solar cell. A transparent substrate;
A surface transparent electrode formed on the transparent substrate;
A plurality of photoelectric conversion layers formed on the surface transparent electrode;
A translucent conductive oxide layer formed on the photoelectric conversion layer,
The surface transparent electrode is formed with a concavo-convex structure having a first period that scatters light in the absorption wavelength region of the first photoelectric conversion layer among the photoelectric conversion layers,
The translucent conductive oxide layer is provided with a concavo-convex structure having a second period that scatters light in the absorption wavelength region of the second photoelectric conversion layer among the photoelectric conversion layers. Thin film solar cell.

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