Solar cell manufacturing method

Abstract

A method for manufacturing a solar cell according to one embodiment of the present invention is provided with: a step for forming a base layer (10) on the surface of a support substrate (100), the surface of which has an uneven structure (101) formed thereon, by applying a varnish; a step for forming a photoelectric conversion structure (20) on the substrate layer (10); and a step for peeling the base material layer (10) from the support substrate (100).

Description

Technical Field

[0001] This invention relates to a method for manufacturing solar cells. Background Technology

[0002] It is known to obtain flexible solar cells by forming a photoelectric conversion layer on a resin film. However, if the resin film flexes or undulates during the formation of the photoelectric conversion layer, it is impossible to form the photoelectric conversion layer with high precision. Therefore, for example, Patent Document 1 proposes a method as follows: coating a precursor onto a support substrate, forming a resin film that adheres tightly to the support substrate by heating, further forming an electrode layer, a photoelectric conversion layer, etc., on the resin film, and then peeling the resin film off the support substrate.

[0003] Furthermore, it is known that by forming an uneven structure on the light-receiving side of a solar cell, light reflection can be reduced and photoelectric conversion efficiency improved. For example, Patent Document 2 describes the following: A photocurable resin composition is coated on a transparent film of a substrate and pressed onto a mold. UV light is irradiated from the back of the transparent film to cure it. Then, the mold is demolded, thereby obtaining a thin-film solar cell substrate with a regular pyramidal shape and tiny uneven shapes that are seamlessly covered. An electrode layer, a photoelectric conversion layer, and a transparent electrode layer are stacked on the uneven surface of this thin-film solar cell substrate, thereby manufacturing a solar cell.

[0004] Patent Document 1: International Publication No. WO2015 / 147106

[0005] Patent Document 2: Japanese Patent Application Publication No. 2010-183000

[0006] In cases where a photoelectric conversion structure is formed on a film with an uneven texture, as in Patent Document 2, the resin film may become flexed or uneven, making it impossible to use a method of forming a thin layer by coating. A method of bonding the film with an uneven texture after forming a photoelectric conversion layer is also considered, but this may result in adverse effects such as a decrease in photoelectric conversion efficiency and an increase in manufacturing costs due to the addition of an adhesive layer in addition to the film with the uneven texture. Summary of the Invention

[0007] Therefore, the objective of this invention is to provide a method for manufacturing solar cells that can produce solar cells with high photoelectric conversion efficiency.

[0008] One aspect of the present invention relates to a method for manufacturing a solar cell, comprising: a step of forming a substrate layer on the surface of a support substrate having an uneven structure formed thereon by applying a varnish; a step of forming a photoelectric conversion structure on the substrate layer; and a step of peeling the substrate layer off the support substrate.

[0009] In the above-described solar cell manufacturing method, the top of the aforementioned uneven structure may also have rounded corners.

[0010] In the above-described solar cell manufacturing method, the supporting substrate may also be a crystalline silicon substrate, and the uneven structure may be an inverted pyramid structure formed by anisotropic etching.

[0011] In the above-described solar cell manufacturing method, the thickness of the substrate layer above the apex of the above-described uneven structure may be 10 μm or less.

[0012] In the above-described solar cell manufacturing method, the process of forming the above-described photoelectric conversion structure may include a process of coating the constituent material or its raw material.

[0013] In the above-described solar cell manufacturing method, the photoelectric conversion structure may also have a p-type semiconductor layer, a photoelectric conversion layer, and an n-type semiconductor layer sequentially from the substrate layer side, and the p-type semiconductor layer or photoelectric conversion layer may be formed by an impregnation method.

[0014] In the above-described solar cell manufacturing method, the p-type semiconductor layer may also be formed from a carbazole phosphate-based material.

[0015] In the above-described solar cell manufacturing method, the supporting substrate may also have: a substrate material; and a passivation layer, which is stacked on the surface of the substrate material to make the top of the uneven structure smooth.

[0016] In the above-described solar cell manufacturing method, the thickness of the passivation layer at the apex of the above-described uneven structure may be greater than the radius of curvature of the surface of the substrate at that apex.

[0017] In the above-described solar cell manufacturing method, the thickness of the passivation layer at the apex of the above-described uneven structure may be greater than the thickness of the passivation layer at the valley of the above-described uneven structure near the apex.

[0018] In the above-described solar cell manufacturing method, the varnish may also be a polyamic acid solution or a polyimide solution.

[0019] According to the solar cell manufacturing method of the present invention, it is possible to manufacture solar cells with high photoelectric conversion efficiency. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the steps of a solar cell manufacturing method according to one embodiment of the present invention.

[0021] Figure 2 It means through Figure 1A schematic cross-sectional view of the structure of a solar cell manufactured by the solar cell manufacturing method.

[0022] Figure 3 It means Figure 1 A schematic cross-sectional view of one step in a method for manufacturing solar cells.

[0023] Figure 4 yes Figure 3 A partially enlarged cross-sectional view of the support substrate.

[0024] Figure 5 It means Figure 1 Solar cell manufacturing method Figure 3 A schematic cross-sectional view illustrating the next step. Detailed Implementation

[0025] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, for convenience, there may be instances where shaded lines, component reference numerals, etc., are omitted; however, in such cases, other drawings should be consulted. Additionally, for ease of observation, the dimensions of various components in the drawings have been adjusted.

[0026] Figure 1 This is a flowchart illustrating the steps of a solar cell manufacturing method according to one embodiment of the present invention. Figure 2 It means through Figure 1 A schematic cross-sectional view of the structure of a solar cell manufactured by the solar cell manufacturing method.

[0027] The solar cell 1 manufactured by the solar cell manufacturing method of this embodiment includes: a substrate layer 10 disposed on the light-receiving surface side; and a photoelectric conversion structure 20 disposed on the back side side of the substrate layer 10.

[0028] The substrate layer 10 is a structural component that ensures the strength of the solar cell 1. The substrate layer 10 is a transparent and flexible resin film. A texture 11 is formed on the light-receiving side of the substrate layer 10, which has tiny bumps and depressions to reduce light reflectivity.

[0029] To reduce light reflection, the texture 11 is preferably formed into a shape covered with numerous pyramidal protrusions. To further reduce light reflection, the top of the texture 11 is preferably formed into a relatively sharp angle. On the other hand, if the valleys of the texture 11 are sharp angles, damage such as breakage may sometimes occur in the substrate layer 10, particularly during the stripping process in the manufacture of the solar cell 1, which will be described later. Therefore, the bottom of the valleys of the texture 11 is preferably rounded.

[0030] The back side region of the substrate layer 10 relative to the valley of the texture 11 ( Figure 2The lower limit of the thickness of the back-side region 12 (the region closer to the back side than the dotted line) is preferably 0.5 μm, more preferably 1 μm. By setting the thickness of the back-side region 12 above the lower limit, the mechanical strength of the solar cell 1 can be guaranteed. The upper limit of the thickness of the back-side region 12 is preferably 10 μm, more preferably 8 μm. By setting the thickness of the back-side region 12 below the upper limit, in addition to cost reduction, the light absorption rate in the back-side region 12 can also be reduced.

[0031] In the illustrated embodiment of the solar cell 1, the photoelectric conversion structure 20 is designed as an inverted perovskite solar cell. In the inverted perovskite solar cell, the photoelectric conversion structure 20 can be configured to sequentially include a first electrode layer 21, a p-type semiconductor layer 22, a photoelectric conversion layer 23, an n-type semiconductor layer 24, and a second electrode layer 25 from the substrate layer 10 side. The first electrode layer 21 is the positive electrode for outputting power. The first electrode layer 21 is preferably made of a transparent conductive oxide (TCO) or similar material that is conductive and transparent. The photoelectric conversion layer 23 absorbs incident light to generate photocarriers (electrons and holes). The p-type semiconductor layer 22 is a hole transport layer that allows holes to pass selectively. The p-type semiconductor layer 22 can be, for example, a self-assembled monolayer composed of materials such as 2PACz ([2-(9H-carbazole-9-yl)ethyl]phosphonic acid), MeO-2PACz ([2-(3,6-dimethoxy-9H-carbazole-9-yl)ethyl]phosphonic acid), or Me-4PACz ([4-(3,6-dimethyl-9H-carbazole-9-yl)butyl]phosphonic acid). The photoelectric conversion layer 23 is a power generation layer that absorbs incident light to generate photocarriers (electrons and holes). The photoelectric conversion layer 23 can be composed of a material containing a perovskite compound. The n-type semiconductor layer 24 is an electron transport layer that allows electrons to pass selectively. The n-type semiconductor layer 24 can be composed of fullerene-based materials, tin oxide-based materials, copper bath, or their laminated films. The second electrode layer 25 is the negative electrode for outputting power. The second electrode layer 25 is preferably composed of a material primarily composed of a metal with low resistance. Alternatively, an oxide buffer layer (not shown), represented by NiOx, can be sandwiched between the first electrode layer 21 and the p-type semiconductor layer 22. The photoelectric conversion structure 20 can also be configured as a sub-module that is divided into multiple sub-units when viewed from above.

[0032] The solar cell manufacturing method of this embodiment includes a substrate layer formation process (step S1), a photoelectric conversion structure formation process (step S2), and a peeling process (step S3).

[0033] In the substrate layer formation process of step S1, such as Figure 3As shown, a substrate layer 10 is formed on the surface of a support substrate 100 by applying a varnish. The support substrate 100 supports intermediate products during manufacturing. A textured surface 101 is formed on the surface of the support substrate 100 (the surface where the substrate layer 10 is formed). This textured surface 101 is macroscopically planar but microscopically has numerous protrusions. Therefore, by transferring the textured surface 101 onto the surface of the substrate layer 10 supported by the support substrate 100, a texture 11 is formed.

[0034] As the support substrate 100, a crystalline silicon substrate is preferably used. If the support substrate 100 is a crystalline silicon substrate, the uneven structure 101 can be formed relatively easily by anisotropic etching. The uneven structure 101 is preferably an inverted pyramid structure (a structure with a pyramidal concave portion). By making the uneven structure 101 an inverted pyramid structure, a texture 11 with a pyramidal structure that captures a lot of light through multiple reflections can be formed on the substrate layer after the peeling process. In addition, by having such an uneven structure 101 act as a foothold, the adhesion between the support substrate 100 and the substrate layer 10 is improved. Therefore, even if the manufacturing process of the solar cell 1 includes a process of immersion in a solution, such as an impregnation method, the solution is difficult to penetrate between the support substrate 100 and the substrate layer 10, and peeling of the substrate layer 10 during the process can be suppressed.

[0035] The lower limit of the maximum height Rz (JIS-B0601) of the uneven structure 101 is preferably 0.5 μm, more preferably 0.8 μm. On the other hand, the upper limit of the maximum height Rz of the uneven structure 101 is preferably 10 μm, more preferably 5 μm. By making the arithmetic mean roughness Rz of the uneven structure 101 above or above the above lower limit, the uneven structure 101 can be accurately transferred to the substrate layer 10, and surface reflection can be reduced. In addition, by making the arithmetic mean roughness Rz of the uneven structure 101 below or below the above upper limit, the light absorption rate of the substrate layer 10 can be relatively low, and cost reduction can be achieved.

[0036] As described above, to make the bottom of the valleys of texture 11 smooth, the top of the uneven structure 101 preferably has rounded corners. Furthermore, to prevent material of the substrate layer 10 from remaining in the valleys of the uneven structure 101 of the supporting substrate 100 during the peeling process, the valleys of the uneven structure 101 preferably also have slightly rounded corners. Therefore, as... Figure 4As shown, the support substrate 100 can be configured to have a substrate 102 and a passivation layer 103, which is stacked on the surface of the substrate 102 to make the top of the uneven structure 101 rounded. The passivation layer 103 is stacked on the sharp uneven surface of the substrate 102 formed by anisotropic etching or the like using methods such as CVD, thereby enabling the top of the uneven structure 101 to have rounded corners. Preferably, the thickness of the passivation layer 103 at the apex of the uneven structure 101 is greater than the radius of curvature of the surface of the substrate 102 at that apex. Furthermore, it is preferable that the thickness of the passivation layer 103 at the apex of the uneven structure 101 is greater than the thickness of the passivation layer 103 at the valley of the uneven structure 101 near that apex.

[0037] In the present inventors' research, when a support substrate 100 without a passivation layer 103 having a rough-textured structure 101 formed by anisotropic etching of the substrate 102 was fabricated using a crystalline silicon substrate as the substrate base 102, the radius of curvature of the apex of the rough-textured structure 101 of the support substrate 100 was 5 nm or less. Therefore, the lower limit of the thickness of the passivation layer 103 is preferably 5 nm, more preferably 10 nm. On the other hand, if the valleys of the rough-textured structure 101 of the substrate layer 10 are excessively rounded, the reflectivity of the substrate layer 10 increases, and it is sometimes difficult to obtain high solar cell characteristics. Therefore, the upper limit of the thickness of the passivation layer 103 is preferably 500 nm or less, more preferably 400 nm or less. By keeping the thickness of the passivation layer 103 below the upper limit, the reflection of the substrate layer 10 can be suppressed. As the material of the passivation layer 103, it is preferable to use a material that has a stronger adhesion strength to the substrate of the support substrate 100 than to the substrate layer 10 and is stable. Examples include oxides, represented by silicon oxides, and nitrides, represented by silicon nitrides.

[0038] As a varnish applied to the surface of the support substrate 100, a polyamic acid solution or a polyimide solution is suitable. The varnish is thinned by coating, firing, and peeling on the surface of the support substrate, enabling the fabrication of a flexible substrate. By coating the support substrate 100 with a polyamic acid solution and heating the coating, a substrate layer 10 made of polyimide with sufficient strength, flexibility, and high light transmittance can be formed. Specifically, the substrate layer formation process preferably includes: coating the support substrate 100 with varnish; and heating the varnish coating on the support substrate 100. Furthermore, the amount of varnish applied is adjusted such that the thickness of the back side region 12, i.e., the thickness of the substrate layer 10 above the apex of the uneven structure 101, falls within the aforementioned range.

[0039] In the photoelectric conversion structure forming process of step S2, such as Figure 5As shown, a photoelectric conversion structure 20 is formed on a substrate layer 10 formed on the surface of a support substrate 100. The photoelectric conversion structure 20 is formed by sequentially stacking a first electrode layer 21, a p-type semiconductor layer 22, a photoelectric conversion layer 23, an n-type semiconductor layer 24, and a second electrode layer 25 according to an appropriate method corresponding to their forming materials. At least one of the p-type semiconductor layer 22, the photoelectric conversion layer 23, and the n-type semiconductor layer 24 can be formed by a method including a step of coating a constituent material (the final desired material) or its raw material (precursor, etc.) as a dispersion or solution, or by a solution method of generating the constituent material in a raw material solution.

[0040] The first electrode layer 21, composed of a transparent conductive oxide, can be stacked, for example, by sputtering, vacuum evaporation, or other methods. The p-type semiconductor layer 22, composed of a self-assembled monolayer, can be formed by a solution coating method, including a carbazole phosphate-based material. Examples of such solution coating methods include spin coating and immersion coating, but immersion coating is preferred from the viewpoint of large area. The photoelectric conversion layer 23 containing a perovskite compound can be formed, for example, by stacking thin films of different materials using coating and drying, and reacting these materials by heating (two-liquid method), or by coating a solution containing a perovskite compound constituent material and crystallizing it using a poor solvent (poor solvent method). In the two-liquid method, an inorganic layer is generally formed as the first layer, and then an organic layer is coated and dried to form the perovskite compound. The organic layer can be formed into a uniform film over a large area by immersing a support substrate 100, in which the substrate layer 10 and other layers and the inorganic layer are formed, in a solution containing its constituent material. Furthermore, in the case of unsuitable solvents, it is preferable to immerse the substrate 100 in a solution containing an unsuitable solvent after coating the substrate 100 with a solution containing a perovskite compound. The n-type semiconductor layer 24 is formed by coating with a solution containing a fullerene-based material, a tin oxide-based material, a copper bath solvent, etc. The second electrode layer 25 can be formed by laminating metals using methods such as sputtering, vacuum evaporation, or plating. Alternatively, the second electrode layer 25 can also be formed by coating and firing with a material containing conductive particles and a binder, such as silver paste.

[0041] In the peeling process of step S3, the substrate layer 10 and the photoelectric conversion structure 20 are peeled off from the support substrate 100 together. That is, in the peeling process, the solar cell 1 formed on the support substrate 100 is separated from the support substrate 100.

[0042] As described above, in the solar cell manufacturing method of this embodiment, a substrate layer 10 is formed by coating a support substrate 100 having a textured structure 101 with a varnish. The textured structure 101 is transferred to the substrate layer 10, forming a texture 11 that suppresses reflection of incident light, improves light absorption, and thus enhances the photoelectric conversion efficiency of the solar cell 1. Furthermore, even processes involving immersion in a solution, such as dipping, can be performed without peeling.

[0043] Furthermore, in the solar cell manufacturing method of this embodiment, a photoelectric conversion structure 20 is formed on a substrate layer 10 formed on and held by a support substrate 100. Therefore, when forming the photoelectric conversion structure 20, the surface of the substrate layer 10 on which the photoelectric conversion structure 20 is formed is kept planar, thus enabling precise formation of the photoelectric conversion structure 20. Particularly when the photoelectric conversion structure 20 includes a coating material step, by keeping the surface to be coated planar, a coating film of uniform thickness can be formed, resulting in a photoelectric conversion structure 20 achieving high photoelectric conversion efficiency.

[0044]

Example

[0045] The present invention will be specifically described below based on embodiments, but the present invention is not limited to the following embodiments.

[0046] As an example, a crystalline silicon substrate with an inverted pyramid-shaped uneven surface formed by anisotropic etching was used as the substrate material. A passivation layer with a thickness of 10 nm was formed on this substrate using plasma CVD, thereby creating a support substrate. A substrate layer with a backside region thickness of 8 μm was formed on this support substrate by coating it with a polyamic acid solution varnish. After forming the photoelectric conversion structure on this substrate layer, the substrate layer was peeled off from the support substrate, thereby enabling the fabrication of a solar cell with high photoelectric conversion efficiency. In addition, solar cells were also prototyped using a support substrate (substrate material) without a passivation layer and a support substrate with a passivation layer thickness of 2 nm. In these cases, if the peeling process is not performed carefully, damage such as breakage may sometimes occur in the substrate layer.

[0047] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments and various modifications and variations are possible. For example, the support substrate may be formed of a material other than crystalline silicon, or a structure with an uneven surface may be formed on the surface of a glass substrate.

[0048] Explanation of reference numerals in the attached figures

[0049] 1…Solar cell; 10…Substrate layer; 11…Texture; 12…Back side region; 20…Photoelectric conversion structure; 21…First electrode layer; 22…P-type semiconductor layer; 23…Photoelectric conversion layer; 24…N-type semiconductor layer; 25…Second electrode layer; 100…Support substrate; 101…Uneven structure; 102…Substrate substrate; 103…Passivation layer.

Claims

1. A method for manufacturing a solar cell, characterized in that, have: The process of forming a substrate layer on the surface of a support substrate with an uneven texture by applying a varnish. The process of forming a photoelectric conversion structure on the substrate layer; and The process of peeling the substrate layer from the support substrate.

2. The method for manufacturing a solar cell according to claim 1, characterized in that, The top of the concave-convex structure has rounded corners.

3. The method for manufacturing a solar cell according to claim 1 or 2, characterized in that, The supporting substrate is a crystalline silicon substrate, and the uneven structure is an inverted pyramid structure formed by anisotropic etching.

4. The method for manufacturing a solar cell according to claim 1 or 2, characterized in that, The thickness of the substrate layer above the apex of the convex-concave structure is less than 10 μm.

5. The method for manufacturing a solar cell according to claim 1 or 2, characterized in that, The process of forming the photoelectric conversion structure includes the process of coating the constituent material or its raw material.

6. The method for manufacturing a solar cell according to claim 1 or 2, characterized in that, The photoelectric conversion structure has a p-type semiconductor layer, a photoelectric conversion layer and an n-type semiconductor layer sequentially from the substrate layer side, and the p-type semiconductor layer or the photoelectric conversion layer is formed by an impregnation method.

7. The method for manufacturing a solar cell according to claim 6, characterized in that, The p-type semiconductor layer is formed of a carbazole phosphate-based material.

8. The method for manufacturing a solar cell according to claim 1 or 2, characterized in that, The supporting substrate has: a substrate material; and a passivation layer, which is stacked on the surface of the substrate material to make the vertices of the uneven structure smooth.

9. The method for manufacturing a solar cell according to claim 8, characterized in that, The thickness of the passivation layer at the apex of the uneven structure is greater than the radius of curvature of the substrate surface at that apex.

10. The method for manufacturing a solar cell according to claim 8, characterized in that, The thickness of the passivation layer at the apex of the convex-concave structure is greater than the thickness of the passivation layer at the valley of the convex-concave structure near that apex.

11. The method for manufacturing a solar cell according to claim 1 or 2, characterized in that, The varnish is a polyamic acid solution or a polyimide solution.

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