WO2024185804A1 - Solar cell element, solar cell module and method for producing solar cell element - Google Patents

Abstract

The present invention provides a solar cell element which has reduced color unevenness of each light-receiving surface when formed into a module. A solar cell element 1 according to the present invention is a back contact solar cell element which is provided with: a crystalline silicon substrate 11 that has a relief structure on the light-receiving surface side; an optical adjustment layer that is formed on the light-receiving surface side of the substrate 11; a first electrode layer and a semiconductor layer that has a first conductivity type, which are formed on a part of the back surface side of the substrate 11; and a second electrode layer and a semiconductor layer that has a second conductivity type, which are formed on another part of the back surface side of the substrate 11. With respect to the substrate 11, the radius of curvature of a top portion of the relief structure in at least a part of a peripheral part Af2 on the light-receiving surface side is larger than the radius of curvature of a top portion of the relief structure in a central part Af1 on the light-receiving surface side. The relief structure of the substrate 11 is reflected in the light-receiving surface of the solar cell element 1. With respect to the solar cell element 1, the radius of curvature of a top portion of the relief structure in at least a part of the peripheral part Af2 on the light-receiving surface side is larger than the radius of curvature of a top portion of the relief structure in the central part Af1 on the light-receiving surface side.

Description

Solar cell, solar cell module, and method for manufacturing solar cell

The present invention relates to solar cells, solar cell modules, and methods for manufacturing solar cells.

There are two types of solar cells: double-sided electrode type solar cells, in which electrodes are formed on both the light-receiving surface and the back surface, and back-surface electrode type (also called back-contact type or back-surface junction type; hereafter referred to as back-contact type) solar cells, in which electrodes are formed only on the back surface. In double-sided electrode type solar cells, electrodes are formed on the light-receiving surface, so the metallic luster of this electrode is noticeable. On the other hand, in back-contact type solar cells, no electrodes are formed on the light-receiving surface, so the light-receiving surface is uniformly black, making it highly aesthetically pleasing. Patent Document 1 discloses a back-contact type solar cell.

For example, a back-contact type solar cell comprises a crystalline silicon substrate, a first conductive type semiconductor layer and a first electrode layer formed in sequence on a portion of the back surface of the substrate, and a second conductive type semiconductor layer and a second electrode layer formed in sequence on another portion of the back surface of the substrate. This solar cell also comprises an optical adjustment layer (anti-reflection layer) formed in sequence on the light-receiving surface side of the substrate.

JP 2014-75526 A

In back-contact solar cells, individual variations occur in the film thickness of the optical adjustment layer on the light-receiving surface due to variations in film-forming conditions or the position within the film-forming device, which results in individual variations in the color of the light-receiving surface.

As mentioned above, in back-contact solar cells, no electrodes are formed on the light-receiving surface. Therefore, in solar cell modules in which multiple back-contact solar cells are arranged in a two-dimensional pattern, color unevenness on the light-receiving surface of these solar cells is easily noticeable.

It is also known that in solar cells, a pyramidal, fine uneven structure known as a texture structure is formed on the light-receiving surface of a crystalline silicon substrate. This reduces the reflection of incident light on the light-receiving surface and improves the light trapping effect in the substrate.

It is known that a textured structure can also be formed on the back side of a crystalline silicon substrate. This increases the efficiency of collecting light that passes through the substrate without being absorbed.

When an uneven structure is formed on the light-receiving surface and back surface of a crystalline silicon substrate, an uneven structure is also formed on the side surface of the crystalline silicon substrate.

When an uneven structure is formed on the light-receiving surface, back surface and side surfaces of a crystalline silicon substrate, cracks, chipping, etc. may occur on the edges of the crystalline silicon substrate (the periphery of the light-receiving surface, the periphery and end surface of the back surface), especially on the side surfaces (end surfaces).

The present invention aims to provide a solar cell, a solar cell module, and a method for manufacturing a solar cell that reduces color unevenness on the individual light receiving surfaces when modularized. The present invention also aims to provide a solar cell and a method for manufacturing a solar cell that reduces chipping.

The inventor(s) of the present application have discovered that in a solar cell module in which multiple solar cells are arranged in a two-dimensional shape, by highlighting the peripheral edge of the light-receiving surface of each solar cell, each solar cell can be viewed three-dimensionally, and this visibility effect makes the color distribution of the light-receiving surface of the multiple solar cells less noticeable.

The solar cell according to the present invention is a back-contact type solar cell including a crystalline silicon substrate having an uneven structure on the light-receiving surface side, an optical adjustment layer formed on the light-receiving surface side of the substrate, a first conductive type semiconductor layer formed on a part of the back surface side of the substrate opposite the light-receiving surface side, a second conductive type semiconductor layer formed on another part of the back surface side of the substrate, a first electrode layer formed on the first conductive type semiconductor layer, and a second electrode layer formed on the second conductive type semiconductor layer, wherein the radius of curvature of the top portion of at least a part of the uneven structure of the peripheral portion of the light-receiving surface side of the substrate is larger than the radius of curvature of the top portion of the uneven structure of the central portion of the light-receiving surface side, the uneven structure of the substrate is reflected in the light-receiving surface of the solar cell, and the radius of curvature of the top portion of at least a part of the uneven structure of the peripheral portion of the light-receiving surface side of the solar cell is larger than the radius of curvature of the top portion of the uneven structure of the central portion of the light-receiving surface side.

In addition, the solar cell module according to the present invention has the above-mentioned solar cells arranged in a two-dimensional manner.

The solar cell manufacturing method according to the present invention is the solar cell manufacturing method described above, in which, in the step of forming an uneven structure on the light-receiving surface side of the crystalline silicon substrate, the flow rate of the etching solution in at least a portion of the periphery of the light-receiving surface side is controlled to be faster than the flow rate of the etching solution in the center of the light-receiving surface side.

In addition, the inventor(s) of the present application discovered that chipping at the edge of the crystalline silicon substrate can be reduced by controlling the radius of curvature of the edge (periphery of the light-receiving surface, periphery of the back surface, and edge face), particularly the top portion of the uneven structure on the side surface (edge face), so that it is larger.

The solar cell according to the present invention is a solar cell comprising a crystalline silicon substrate having an uneven structure on the light-receiving surface side, back surface side and side surface, a first conductive type semiconductor layer formed on the light-receiving surface side or back surface side of the substrate, a second conductive type semiconductor layer formed on the light-receiving surface side or back surface side of the substrate, a first electrode layer formed on the first conductive type semiconductor layer, and a second electrode layer formed on the second conductive type semiconductor layer, wherein the radius of curvature of the top portion of the uneven structure on the side surface of the substrate is greater than the radius of curvature of the top portion of the uneven structure in the center of the light-receiving surface side and the radius of curvature of the top portion of the uneven structure in the center of the back surface side.

The solar cell manufacturing method according to the present invention is the solar cell manufacturing method described above, in which, in the process of forming an uneven structure on the light-receiving surface side, back surface side, and side surface side of the crystalline silicon substrate, the flow rate of the etching solution on at least a portion of the periphery of the light-receiving surface side and on the side surface is controlled to be faster than the flow rate of the etching solution in the center of the light-receiving surface side, and the flow rate of the etching solution on at least a portion of the periphery of the back surface side and on the side surface is controlled to be faster than the flow rate of the etching solution in the center of the back surface side.

According to the present invention, it is possible to reduce color unevenness on the light receiving surface of each solar cell in a modularized system. In addition, according to the present invention, it is possible to reduce chipping in solar cells.

1 is a diagram showing a solar cell module according to a first embodiment as viewed from the light receiving surface side. 1 is a diagram showing a solar cell according to a first embodiment as viewed from the light-receiving surface side. 1 is a diagram showing a solar cell according to a first embodiment as viewed from the back surface side. 4 is a cross-sectional view taken along line IV-IV of the solar cell shown in FIG. 3. 3 is a cross-sectional view showing an uneven structure in the center of the light-receiving surface side of the substrate shown in FIG. 2. 3 is a cross-sectional view showing an uneven structure of a peripheral portion on a light-receiving surface side of the substrate shown in FIG. 2. 4 is a cross-sectional view showing an uneven structure in the center of the rear surface side of the substrate shown in FIG. 3. 4 is a cross-sectional view showing an uneven structure of the peripheral portion on the back surface side of the substrate shown in FIG. 3. 4 is a cross-sectional view showing the uneven structure on the side surface of the substrate shown in FIGS. 2 and 3. FIG. 13 is a diagram showing a solar cell module according to a modified example of the first embodiment, viewed from the light receiving surface side. FIG. 13 is a view of a solar cell according to a modified example of the first embodiment, viewed from the light-receiving surface side. FIG. 3 is a cross-sectional view showing an uneven structure in the center of the light-receiving surface side of the substrate shown in FIG. 2 (second embodiment); 3 is a cross-sectional view showing an uneven structure of a peripheral portion on the light-receiving surface side of the substrate shown in FIG. 2 (second embodiment);

Below, an example of an embodiment of the present invention will be described with reference to the attached drawings. Note that the same reference numerals will be used to refer to the same or equivalent parts in each drawing. For convenience, hatching and component reference numerals may be omitted, in which case other drawings should be referenced.

[First embodiment]
(Solar cell module)
Fig. 1 is a view of a solar cell module according to a first embodiment as viewed from the light receiving surface side. The solar cell module 100 shown in Fig. 1 includes a plurality of solar cells 1 arranged two-dimensionally at equal intervals. The solar cells 1 are connected in series and/or parallel by known interconnectors (not shown), such as tabs. The solar cells 1 are sealed by a light receiving surface protection member, a back surface protection member, and a sealing material (not shown).

(Solar cell)
Fig. 2 is a view of the solar cell according to the first embodiment as viewed from the light-receiving surface side, Fig. 3 is a view of the solar cell according to the first embodiment as viewed from the back surface side, and Fig. 4 is a cross-sectional view of the solar cell shown in Fig. 3 along line IV-IV. The solar cell 1 shown in Figs. 2 to 4 is a back-contact type (also called back surface junction type or back surface electrode type) heterojunction solar cell. The solar cell 1 includes a crystalline silicon substrate 11 having two main surfaces, and the main surface of the substrate 11 has a first region 7 and a second region 8.

The first region 7 has a so-called comb-like shape and has multiple finger portions 7f that correspond to the teeth of the comb, and busbar portions 7b that correspond to the supports of the teeth of the comb. The busbar portions 7b extend in a first direction (X direction) along one side of the substrate 11, and the finger portions 7f extend from the busbar portions 7b in a second direction (Y direction) that intersects with the first direction.

Similarly, the second region 8 has a so-called comb shape, and has multiple finger portions 8f that correspond to the teeth of the comb, and a busbar portion 8b that corresponds to the support portion of the teeth of the comb. The busbar portion 8b extends in a first direction (X direction) along one side portion of the substrate 11 that faces the other side portion, and the finger portion 8f extends in a second direction (Y direction) from the busbar portion 8b.

The finger portions 7f and 8f are strip-shaped extending in the second direction (Y direction) and are arranged alternately in the first direction (X direction). The first region 7 and the second region 8 may be formed in a stripe pattern.

As shown in FIG. 4, the solar cell 1 comprises a crystalline silicon substrate 11, and a passivation layer 13 and an optical adjustment layer 15, which are stacked in this order on the light-receiving surface side of the substrate 11. The solar cell 1 also comprises a passivation layer 23, a first conductivity type semiconductor layer 25, and a first electrode layer 27, which are stacked in this order on a portion (first region 7) of the back surface side of the substrate 11. The solar cell 1 also comprises a passivation layer 33, a second conductivity type semiconductor layer 35, and a second electrode layer 37, which are stacked in this order on another portion (second region 8) of the back surface side of the substrate 11.

The substrate 11 is formed of a crystalline silicon material such as single crystal silicon or polycrystalline silicon. The substrate 11 is, for example, an n-type substrate in which a crystalline silicon material is doped with an n-type dopant. The substrate 11 may be, for example, a p-type substrate in which a crystalline silicon material is doped with a p-type dopant. An example of an n-type dopant is phosphorus (P). An example of a p-type dopant is boron (B). The substrate 11 functions as a photoelectric conversion substrate that absorbs incident light from the light-receiving surface side and generates photocarriers (electrons and holes).

By using crystalline silicon as the material for the substrate 11, the dark current is relatively small, and a relatively high output (stable output regardless of illuminance) can be obtained even when the intensity of the incident light is low.

The substrate 11 has a pyramidal micro-uneven structure, known as a texture structure, on the light-receiving surface side. This reduces the reflection of incident light on the light-receiving surface, improving the light trapping effect of the substrate 11.

In addition, the back side of the substrate 11 has a pyramidal, fine uneven structure called a texture structure. This increases the efficiency of collecting light that passes through the substrate 11 without being absorbed.

In addition, the side surface of the substrate 11 has a pyramidal, fine uneven structure called a texture structure.

Passivation layer 13 is formed on the light-receiving surface side of substrate 11. Passivation layer 23 is formed in first region 7 on the back side of substrate 11. Passivation layer 33 is formed in second region 8 on the back side of substrate 11. Passivation layers 13, 23, and 33 are formed of a material whose main component is, for example, an intrinsic (i-type) amorphous silicon material. Passivation layers 13, 23, and 33 suppress recombination of carriers generated in substrate 11 and increase carrier recovery efficiency.

The optical adjustment layer 15 is formed on the passivation layer 13 on the light-receiving surface side of the substrate 11. The optical adjustment layer 15 functions as an anti-reflection layer that prevents reflection of incident light, and also functions as a protective layer that protects the light-receiving surface side of the substrate 11 and the passivation layer 13. The optical adjustment layer 15 is formed of an insulating material, for example, silicon oxide (SiO), silicon nitride (SiN), or a composite thereof such as silicon oxynitride (SiON).

The first conductive type semiconductor layer 25 is formed on the passivation layer 23, i.e., in the first region 7 on the back side of the substrate 11. On the other hand, the second conductive type semiconductor layer 35 is formed on the passivation layer 33, i.e., in the second region 8 on the back side of the substrate 11. That is, the first conductive type semiconductor layer 25 and the second conductive type semiconductor layer 35 have a band-like shape and extend in the Y direction. The first conductive type semiconductor layer 25 and the second conductive type semiconductor layer 35 are alternately arranged in the X direction. A portion of the second conductive type semiconductor layer 35 may overlap a portion of the adjacent first conductive type semiconductor layer 25 (not shown).

The first conductive type semiconductor layer 25 is formed, for example, from an amorphous silicon material. The first conductive type semiconductor layer 25 is, for example, a p-type semiconductor layer in which an amorphous silicon material is doped with a p-type dopant (for example, the above-mentioned boron (B)).

The second conductive type semiconductor layer 35 is formed, for example, from an amorphous silicon material. The second conductive type semiconductor layer 35 is, for example, an n-type semiconductor layer in which an amorphous silicon material is doped with an n-type dopant (for example, the above-mentioned phosphorus (P)). Note that the first conductive type semiconductor layer 25 may be an n-type semiconductor layer, and the second conductive type semiconductor layer 35 may be a p-type semiconductor layer.

The first electrode layer 27 is formed on the first conductive type semiconductor layer 25, i.e., in the first region 7 on the back side of the substrate 11. On the other hand, the second electrode layer 37 is formed on the second conductive type semiconductor layer 35, i.e., in the second region 8 on the back side of the substrate 11. In other words, the first electrode layer 27 and the second electrode layer 37 are strip-shaped and extend in the Y direction. The first electrode layer 27 and the second electrode layer 37 are alternately provided in the X direction.

The first electrode layer 27 is formed on the first conductivity type semiconductor layer 25, and the second electrode layer 37 is formed on the second conductivity type semiconductor layer 35. The first electrode layer 27 has a transparent electrode layer 28 and a metal electrode layer 29 formed in that order on the first conductivity type semiconductor layer 25. The second electrode layer 37 has a transparent electrode layer 38 and a metal electrode layer 39 formed in that order on the second conductivity type semiconductor layer 35.

The transparent electrode layers 28, 38 are formed from a transparent conductive material. Examples of transparent conductive materials include ITO (Indium Tin Oxide: a composite oxide of indium oxide and tin oxide). The metal electrode layers 29, 39 are formed from a conductive paste material containing, for example, a metal powder such as silver.

Next, the uneven structure of the substrate 11 will be described with reference to Figs. 2 to 9. Fig. 5 is a cross-sectional view showing the uneven structure of the central portion Af1 on the light-receiving surface side of the substrate 11 shown in Fig. 2, and Fig. 6 is a cross-sectional view showing the uneven structure of the peripheral portion Af2 on the light-receiving surface side of the substrate 11 shown in Fig. 2. Fig. 7 is a cross-sectional view showing the uneven structure of the central portion Ar1 on the back surface side of the substrate 11 shown in Fig. 3, and Fig. 8 is a cross-sectional view showing the uneven structure of the peripheral portion Ar2 on the back surface side of the substrate 11 shown in Fig. 3. Fig. 9 is a cross-sectional view showing the uneven structure of the side surface As of the substrate 11 shown in Figs. 2 and 3.

As shown in Figures 2, 5 and 6, in the substrate 11, the radius of curvature Rf2 of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side is larger than the radius of curvature Rf1 of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side. The uneven structure of the substrate 11 is reflected in the light-receiving surface of the solar cell 1. As a result, in the solar cell 1, the radius of curvature of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side is larger than the radius of curvature of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side.

In addition, in the passivation layer 13 and the optical adjustment layer 15 of the solar cell 1, the film thickness of the peripheral portion Af2 on the light-receiving surface side is thinner than the film thickness of the central portion Af1 on the light-receiving surface side.

Also, as shown in Figures 3, 7, and 8, in the substrate 11, the radius of curvature Rr2 of the top portion of the uneven structure in the peripheral portion Ar2 on the back side is larger than the radius of curvature Rr1 of the top portion of the uneven structure in the central portion Ar1 on the back side.

Furthermore, as shown in FIG. 9, when the radius of curvature of the top portion of the uneven structure on the side surface As of the substrate 11 is taken as Rs, these radii of curvature satisfy the following relational expression.
Rs>Rf2>Rf1>Rr2>Rr1

(Method of manufacturing solar cell)
A method for manufacturing the solar cell 1 according to the first embodiment shown in FIGS. 2 to 9 will now be described.

First, anisotropic etching is performed on the light-receiving surface side and back surface side of the crystalline silicon substrate 11 to form a pyramidal fine uneven structure called a texture structure (crystalline silicon substrate formation process). At this time, anisotropic etching is also performed on the side surface of the crystalline silicon substrate 11, and a pyramidal fine uneven structure is formed in the same way as on the light-receiving surface side and back surface side. An example of the etching solution is an alkaline solution such as an aqueous solution of potassium hydroxide.

At this time, the flow rate of the etching solution in the peripheral portion Af2 on the light-receiving surface side is controlled to be faster than the flow rate of the etching solution in the central portion Af1 on the light-receiving surface side. Also, the flow rate of the etching solution in the peripheral portion Ar2 on the back surface side is controlled to be faster than the flow rate of the etching solution in the central portion Ar1 on the back surface side.

As a result, the radius of curvature Rf1 of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side, the radius of curvature Rf2 of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side, the radius of curvature Rr1 of the top portion of the uneven structure of the central portion Ar1 on the back surface side, the radius of curvature Rr2 of the top portion of the uneven structure of the peripheral portion Ar2 on the back surface side, and the radius of curvature Rs of the top portion of the uneven structure on the side surface As satisfy the following relationship.
Rs>Rf2>Rf1>Rr2>Rr1

Next, the passivation layer 13 and the optical adjustment layer 15 are formed on the entire light receiving surface of the substrate 11 (optical adjustment layer formation process). The passivation layer 13 and the optical adjustment layer 15 can be formed, for example, by CVD (chemical vapor deposition) or PVD (physical vapor deposition).

At this time, the uneven structure of the substrate 11 is reflected on the light-receiving surface of the solar cell 1, and the radius of curvature of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side of the solar cell 1 is greater than the radius of curvature of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side. Also, in the passivation layer 13 and optical adjustment layer 15 of the solar cell 1, the film thickness of the peripheral portion Af2 on the light-receiving surface side is thinner than the film thickness of the central portion Af1 on the light-receiving surface side.

Next, a passivation layer 23 and a first conductive type semiconductor layer 25 are formed on a portion of the back surface of the substrate 11, specifically in the first region 7 (semiconductor layer formation process). For example, a passivation layer material film and a first conductive type semiconductor layer material film may be formed on the entire back surface of the substrate 11 using a CVD method or a PVD method, and then the passivation layer 23 and the first conductive type semiconductor layer 25 may be patterned using a resist generated using a photolithography technique or a printing technique, or an etching method using a metal mask.

Incidentally, examples of etching solutions for p-type semiconductor layer material films include acidic solutions such as hydrofluoric acid containing ozone or a mixture of nitric acid and hydrofluoric acid, and examples of etching solutions for n-type semiconductor layer material films include alkaline solutions such as an aqueous solution of potassium hydroxide.

Alternatively, when a passivation layer and a first conductive type semiconductor layer are laminated on the back side of the substrate 11 using a CVD method or a PVD method, a mask may be used to simultaneously form and pattern the passivation layer 23 and the first conductive type semiconductor layer 25.

Next, a passivation layer 33 and a second conductive type semiconductor layer 35 are formed on another part of the back side of the substrate 11, specifically in the second region 8 (semiconductor layer formation process). For example, as described above, a passivation layer material film and a second conductive type semiconductor layer material film may be formed on the entire back side of the substrate 11 using a CVD method or a PVD method, and then the passivation layer 33 and the second conductive type semiconductor layer 35 may be patterned using a resist generated using a photolithography technique or a printing technique, or an etching method using a metal mask.

Alternatively, when a passivation layer and a second conductive type semiconductor layer are laminated on the back side of the substrate 11 using a CVD method or a PVD method, a mask may be used to simultaneously form and pattern the passivation layer 33 and the second conductive type semiconductor layer 35.

The order in which the passivation layers 13, 23, 33, the optical adjustment layer 15, the first conductive type semiconductor layer 25, and the second conductive type semiconductor layer 35 are formed is not limited.

Next, a first electrode layer 27 and a second electrode layer 37 are formed on the first conductive type semiconductor layer 25 and the second conductive type semiconductor layer 35 on the back side of the substrate 11, specifically in the first region 7 and the second region 8 (electrode layer formation process).

For example, a transparent electrode layer material film may be formed on the entire back surface of the substrate 11 using a CVD or PVD method, and then the transparent electrode layers 28, 38 may be patterned using a resist generated using a photolithography or printing technique, or an etching method using a metal mask. As an etching solution for the transparent electrode layer material film, for example, hydrochloric acid or an aqueous solution of ferric chloride is used.

Then, for example, using a pattern printing method or a coating method, a metal electrode layer 29 is formed on the transparent electrode layer 28, and a metal electrode layer 39 is formed on the transparent electrode layer 38, thereby forming the first electrode layer 27 and the second electrode layer 37.
Through the above steps, the back contact type solar cell 1 according to the first embodiment shown in FIGS. 2 to 9 is completed.

As described above, in the solar cell 1 of the first embodiment, in the substrate 11, the radius of curvature Rf2 of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side is larger than the radius of curvature Rf1 of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side, and the uneven structure of the substrate 11 is reflected in the light-receiving surface of the solar cell 1, and in the solar cell 1, the radius of curvature of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side is larger than the radius of curvature of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side.

In this way, by controlling the radius of curvature Rf2 of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side to be larger, the reflection of light at the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side increases, and it appears white, for example. In this way, by controlling the texture shape of the peripheral portion Af2 on the light-receiving surface side and deliberately making the peripheral portion Af2 on the light-receiving surface side of the solar cell 1 stand out, the solar cell 1 can be viewed three-dimensionally within the solar cell module 100, and the color distribution inside the solar cell module 100 becomes less noticeable.

Furthermore, according to the solar cell 1 of the first embodiment, in the optical adjustment layer 15, the film thickness of the peripheral portion Af2 on the light-receiving surface side is thinner than the film thickness of the central portion Af1 on the light-receiving surface side. In this way, when the film thickness of the peripheral portion Af2 on the light-receiving surface side becomes thinner, the reflection of light at the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side increases, and for example, it appears white.

In this way, by controlling the thickness of the optical adjustment layer 15 in addition to the texture shape of the peripheral portion Af2 on the light receiving surface side, and deliberately making the peripheral portion Af2 on the light receiving surface side of the solar cell 1 stand out, the solar cell 1 can be viewed three-dimensionally within the solar cell module 100, and the color distribution inside the solar cell module 100 becomes less noticeable.

If an uneven structure is formed on the light receiving surface and/or back surface of the substrate 11, chipping may occur at the edge of the substrate 11.

In this regard, according to the solar cell 1 of the first embodiment, in the substrate 11, the radius of curvature Rf2 of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side is larger than the radius of curvature Rf1 of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side. Also, in the substrate 11, the radius of curvature Rr2 of the top portion of the uneven structure of the peripheral portion Ar2 on the back surface side is larger than the radius of curvature Rr1 of the top portion of the uneven structure of the central portion Ar1 on the back surface side. Also, these radii of curvature satisfy the following relational expression.
Rf2>Rf1>Rr2>Rr1

In this way, by controlling the radius of curvature Rf2 of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side to be larger, chipping at the edge of the substrate 11 can be reduced. This makes it possible to improve the productivity of the solar cell 1. In addition, by controlling the radius of curvature Rr2 of the top portion of the uneven structure of the peripheral portion Ar2 on the back surface side to be larger, chipping at the edge of the substrate 11 can be reduced. This makes it possible to improve the productivity of the solar cell 1.

Here, anisotropic etching forms an uneven structure not only on the light-receiving surface and back surface of the substrate 11, but also on the side surfaces (end surfaces). Furthermore, chipping is likely to occur in the uneven structure on the side surfaces of the ends of the substrate 11 (periphery of the light-receiving surface, periphery of the back surface, side surfaces).

In this regard, in the solar cell 1 of the first embodiment, when the radius of curvature of the top portion of the uneven structure on the side surface of the substrate 11 is taken as Rs, these radii of curvature satisfy the following relational expression.
Rs>Rf2>Rf1>Rr2>Rr1

In this way, by controlling the radius of curvature Rs to be large, particularly at the top of the uneven structure on the side surface, chipping at the edge of the substrate 11 can be reduced. This makes it possible to improve the productivity of the solar cell 1.

The above describes the first embodiment of the present invention, but the present invention is not limited to the above-mentioned first embodiment and various modifications and variations are possible. For example, the above-mentioned first embodiment illustrates a form in which a large-sized semiconductor substrate (wafer) of a specified size (e.g., a 6-inch semi-square shape) is used as is. However, the present invention is not limited to this, and may be a form in which a half-cut solar cell is used in which a large-sized semiconductor substrate of a specified size is cut into two pieces, as shown in Figures 10 and 11, or a form in which a solar cell is used in which a large-sized semiconductor substrate of a specified size is cut into three or more pieces.

In this case, in the substrate 11, it is sufficient that the radius of curvature Rf2 of the top portion of the uneven structure of at least a portion of the peripheral portion Af2 on the light-receiving surface side is larger than the radius of curvature Rf1 of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side, and in the solar cell 1, it is sufficient that the radius of curvature of the top portion of the uneven structure of at least a portion of the peripheral portion Af2 on the light-receiving surface side is larger than the radius of curvature of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side. Also, in the optical adjustment layer 15, it is sufficient that the film thickness of at least a portion of the peripheral portion Af2 on the light-receiving surface side is thinner than the film thickness of the central portion Af1 on the light-receiving surface side.

In addition, in the substrate 11, it is sufficient that the radius of curvature Rr2 of the apex portion of the uneven structure of at least a part of the peripheral portion Ar2 on the back side is larger than the radius of curvature Rr1 of the apex portion of the uneven structure of the central portion Ar1 on the back side. Furthermore, it is sufficient that these radii of curvature satisfy the following relational expression.
Rs>Rf2>Rf1>Rr2>Rr1

[Second embodiment]
In the above-described first embodiment, a configuration has been described in which each radius of curvature satisfies the following relational expression in order to make the color distribution inside the solar cell module 100 less noticeable and to reduce chipping at the end of the substrate 11.
Rs>Rf2>Rf1>Rr2>Rr1

In the second embodiment, a configuration in which each radius of curvature satisfies the following relational expression in order to reduce chipping at the end of the substrate 11 will be described.
Rs>Rf2>Rf1
Rs>Rr2>Rr1

(Solar cell module)
The configuration of the solar cell module 100 according to the second embodiment is the same as the configuration of the solar cell module 100 according to the first embodiment shown in FIG.

(Solar cell)
The configuration of the solar cell 1 according to the second embodiment is the same as the configuration of the solar cell 1 according to the first embodiment shown in FIGS. 2 to 4, except for the following points.

Next, the uneven structure of the substrate 11 will be described with reference to Figures 2 to 4, 12 to 13, and 7 to 9. Figure 12 is a cross-sectional view showing the uneven structure of the central portion Af1 on the light-receiving surface side of the substrate 11 shown in Figure 2, and Figure 13 is a cross-sectional view showing the uneven structure of the peripheral portion Af2 on the light-receiving surface side of the substrate 11 shown in Figure 2.

As shown in Figures 2, 12, and 13, in the substrate 11, the radius of curvature Rf2 of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side is larger than the radius of curvature Rf1 of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side.

Also, as shown in Figures 3, 7, and 8, in the substrate 11, the radius of curvature Rr2 of the top portion of the uneven structure in the peripheral portion Ar2 on the back side is larger than the radius of curvature Rr1 of the top portion of the uneven structure in the central portion Ar1 on the back side.

Furthermore, as shown in FIG. 9, when the radius of curvature of the top portion of the uneven structure on the side surface As of the substrate 11 is taken as Rs, these radii of curvature satisfy the following relational expression.
Rs>Rf2>Rf1
Rs>Rr2>Rr1

In other words, in the substrate 11, the radius of curvature Rs of the top portion of the uneven structure on the side As is greater than the radius of curvature Rf1 of the top portion of the uneven structure on the central portion Af1 on the light receiving surface side, and the radius of curvature Rr1 of the top portion of the uneven structure on the central portion Ar1 on the back surface side.

(Method of manufacturing solar cell)
A method for manufacturing the solar cell 1 according to this embodiment shown in FIGS. 2 to 4, 12 to 13, and 7 to 9 will now be described.

First, anisotropic etching is performed on the light receiving surface side and back surface side of the crystalline silicon substrate 11 to form a pyramidal fine uneven structure called a texture structure (crystalline silicon substrate formation process). At this time, anisotropic etching is also performed on the side surface of the crystalline silicon substrate 11 to form a pyramidal fine uneven structure called a texture structure. An example of the etching solution is an alkaline solution such as an aqueous solution of potassium hydroxide.

At this time, the flow rate of the etching solution in the peripheral portion Af2 on the light-receiving surface side is controlled to be faster than the flow rate of the etching solution in the central portion Af1 on the light-receiving surface side. Also, the flow rate of the etching solution in the peripheral portion Ar2 on the back surface side is controlled to be faster than the flow rate of the etching solution in the central portion Ar1 on the back surface side.

As a result, the radius of curvature Rf1 of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side, the radius of curvature Rf2 of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side, the radius of curvature Rr1 of the top portion of the uneven structure of the central portion Ar1 on the back surface side, the radius of curvature Rr2 of the top portion of the uneven structure of the peripheral portion Ar2 on the back surface side, and the radius of curvature Rs of the top portion of the uneven structure on the side surface As satisfy the following relationship.
Rs>Rf2>Rf1
Rs>Rr2>Rr1

Next, the passivation layer 13 and the optical adjustment layer 15 are formed on the entire light receiving surface of the substrate 11 (optical adjustment layer formation process). The passivation layer 13 and the optical adjustment layer 15 can be formed, for example, by CVD (chemical vapor deposition) or PVD (physical vapor deposition).

Next, a passivation layer 23 and a first conductive type semiconductor layer 25 are formed on a portion of the back side of the substrate 11, specifically in the first region 7 (semiconductor layer formation process). For example, a passivation layer material film and a first conductive type semiconductor layer material film may be formed on the entire back side of the substrate 11 using a CVD method or a PVD method, and then the passivation layer 23 and the first conductive type semiconductor layer 25 may be patterned using a resist generated using a photolithography technique or a printing technique, or an etching method using a metal mask.

Incidentally, examples of etching solutions for p-type semiconductor layer material films include acidic solutions such as hydrofluoric acid containing ozone or a mixture of nitric acid and hydrofluoric acid, and examples of etching solutions for n-type semiconductor layer material films include alkaline solutions such as an aqueous solution of potassium hydroxide.

Alternatively, when a passivation layer and a first conductive type semiconductor layer are laminated on the back side of the substrate 11 using a CVD method or a PVD method, a mask may be used to simultaneously form and pattern the passivation layer 23 and the first conductive type semiconductor layer 25.

Next, a passivation layer 33 and a second conductive type semiconductor layer 35 are formed on another part of the back side of the substrate 11, specifically in the second region 8 (semiconductor layer formation process). For example, as described above, a passivation layer material film and a second conductive type semiconductor layer material film may be formed on the entire back side of the substrate 11 using a CVD method or a PVD method, and then the passivation layer 33 and the second conductive type semiconductor layer 35 may be patterned using a resist generated using a photolithography technique or a printing technique, or an etching method using a metal mask.

Alternatively, when a passivation layer and a second conductive type semiconductor layer are laminated on the back side of the substrate 11 using a CVD method or a PVD method, a mask may be used to simultaneously form and pattern the passivation layer 33 and the second conductive type semiconductor layer 35.

The order in which the passivation layers 13, 23, 33, the optical adjustment layer 15, the first conductive type semiconductor layer 25, and the second conductive type semiconductor layer 35 are formed is not limited.

Next, a first electrode layer 27 and a second electrode layer 37 are formed on the first conductive type semiconductor layer 25 and the second conductive type semiconductor layer 35 on the back side of the substrate 11, specifically in the first region 7 and the second region 8 (electrode layer formation process).

For example, a transparent electrode layer material film may be formed on the entire back surface of the substrate 11 using a CVD or PVD method, and then the transparent electrode layers 28, 38 may be patterned using a resist generated using a photolithography or printing technique, or an etching method using a metal mask. An example of an etching solution for the transparent electrode layer material film is an aqueous solution of hydrochloric acid or ferric chloride.

Thereafter, for example, using a pattern printing method or a coating method, a metal electrode layer 29 is formed on the transparent electrode layer 28, and a metal electrode layer 39 is formed on the transparent electrode layer 38, thereby forming the first electrode layer 27 and the second electrode layer 37.
Through the above steps, the back contact type solar cell 1 according to this embodiment shown in FIGS. 2 to 4, 12 to 13, and 7 to 9 is completed.

Here, when a concave-convex structure is formed on the light-receiving surface and/or the back surface of the substrate 11, chipping may occur at the edge of the substrate 11.
Here, anisotropic etching forms an uneven structure not only on the light-receiving surface and back surface but also on the side surfaces (end surfaces) of substrate 11. Among the ends of substrate 11 (periphery of the light-receiving surface, peripheral portion of the back surface, and side surfaces), chipping is likely to occur in the uneven structure on the side surfaces.

In this regard, according to the solar cell 1 of the second embodiment, in the substrate 11, the radius of curvature Rs of the top portion of the uneven structure on the side surface As is larger than the radius of curvature Rf1 of the top portion of the uneven structure on the central portion Af1 on the light-receiving surface side, and the radius of curvature Rr1 of the top portion of the uneven structure on the central portion Ar1 on the back surface side. As a result, by controlling the radius of curvature Rs of the top portion of the uneven structure on the side surface in particular to be larger, chipping at the edge of the substrate 11 can be reduced. This makes it possible to improve the productivity of the solar cell 1.

Furthermore, according to the solar cell 1 of the second embodiment, in the substrate 11, the radius of curvature Rf2 of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side is larger than the radius of curvature Rf1 of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side. In this way, by controlling the radius of curvature Rf2 of the top portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side to be larger, chipping of the edge of the substrate 11 can be reduced. As a result, the productivity of the solar cell 1 can be improved.

According to the knowledge of the present inventor(s), chipping is likely to occur in the uneven structure of the side surface among the ends (periphery of the light receiving surface, peripheral portion of the back surface, and side surfaces) of the substrate 11. Therefore, it is preferable that the radii of curvature of these satisfy the following relational expression.
Rs>Rf2>Rf1

Furthermore, according to the solar cell 1 of the second embodiment, in the substrate 11, the radius of curvature Rr2 of the top portion of the uneven structure of the peripheral portion Ar2 on the back side is larger than the radius of curvature Rr1 of the top portion of the uneven structure of the central portion Ar1 on the back side. In this way, by controlling the radius of curvature Rr2 of the top portion of the uneven structure of the peripheral portion Ar2 on the back side to be larger, chipping at the edge of the substrate 11 can be reduced. As a result, the productivity of the solar cell 1 can be improved.

According to the knowledge of the present inventor(s), chipping is likely to occur in the uneven structure of the side surface among the ends (periphery of the light receiving surface, peripheral portion of the back surface, and side surfaces) of the substrate 11. Therefore, it is preferable that the radii of curvature of these satisfy the following relational expression.
Rs>Rr2>Rr1

The second embodiment of the present invention has been described above, but the present invention is not limited to the above-mentioned second embodiment, and various modifications and variations are possible. For example, the above-mentioned second embodiment illustrates a form in which a large-sized semiconductor substrate (wafer) of a specified size (e.g., a 6-inch semi-square shape) is used as is. However, the present invention is not limited to this, and may be a form in which a half-cut solar cell is used in which a large-sized semiconductor substrate of a specified size is cut into two pieces, as shown in Figures 10 and 11, or a form in which a solar cell is used in which a large-sized semiconductor substrate of a specified size is cut into three or more pieces.

In this case, in the substrate 11, the radius of curvature Rf2 of the top portion of at least a portion of the uneven structure of the peripheral portion Af2 on the light-receiving surface side should be larger than the radius of curvature Rf1 of the top portion of the uneven structure of the central portion Af1 on the light-receiving surface side.

Furthermore, in the substrate 11, the radius of curvature Rr2 of the top portion of at least a portion of the uneven structure in the peripheral portion Ar2 on the back side may be greater than the radius of curvature Rr1 of the top portion of the uneven structure in the central portion Ar1 on the back side.

In addition, in the second embodiment described above, a back-contact type solar cell is exemplified. However, the present invention is not limited to this, and can also be applied to a double-sided electrode type solar cell.

REFERENCE SIGNS LIST 1 solar cell 7 first region 7f finger portion 7b busbar portion 8 second region 8f finger portion 8b busbar portion 11 crystalline silicon substrate 13, 23, 33 passivation layer 15 optical adjustment layer 25 first conductive type semiconductor layer 27 first electrode layer 28 first transparent electrode layer 29 first metal electrode layer 35 second conductive type semiconductor layer 37 second electrode layer 38 second transparent electrode layer 39 second metal electrode layer 100 solar cell module

Claims (13)

a crystalline silicon substrate having an uneven structure on a light receiving surface side;
an optical adjustment layer formed on the light receiving surface side of the substrate;
a first conductive type semiconductor layer formed on a part of a back surface side of the substrate opposite to the light receiving surface side;
a second conductive type semiconductor layer formed on another part of the back surface side of the substrate;
a first electrode layer formed on the first conductive type semiconductor layer;
a second electrode layer formed on the second conductive type semiconductor layer;
A back contact type solar cell comprising:
In the substrate, a radius of curvature of a top portion of at least a part of the concave-convex structure in a peripheral portion on the light receiving surface side is larger than a radius of curvature of a top portion of the concave-convex structure in a central portion on the light receiving surface side,
The light receiving surface of the solar cell reflects the uneven structure of the substrate,
In the solar cell, a radius of curvature of a top portion of the uneven structure of at least a part of the peripheral portion on the light receiving surface side is larger than a radius of curvature of a top portion of the uneven structure of a central portion on the light receiving surface side.
Solar cell. The solar cell according to claim 1, wherein the thickness of at least a portion of the optical adjustment layer at the periphery on the light receiving surface side is thinner than the thickness of the central portion on the light receiving surface side. The substrate has a concave-convex structure on the back surface side,
The solar cell according to claim 1 or 2, wherein in the substrate, the radius of curvature of the top portion of the uneven structure of at least a portion of the peripheral portion on the back surface side is larger than the radius of curvature of the top portion of the uneven structure of the central portion on the back surface side. In the substrate, if the radius of curvature of the apex portion of the concave-convex structure in the central portion on the light-receiving surface side is Rf1, the radius of curvature of the apex portion of at least a portion of the concave-convex structure in the peripheral portion on the light-receiving surface side is Rf2, the radius of curvature of the apex portion of the concave-convex structure in the central portion on the back surface side is Rr1, and the radius of curvature of the apex portion of at least a portion of the concave-convex structure in the peripheral portion on the back surface side is Rr2, these radii of curvature satisfy the following relational expression:
Rf2>Rf1>Rr2>Rr1
The solar cell according to claim 3 . The substrate has a concave-convex structure on a side surface thereof,
In the substrate, when the radius of curvature of the top portion of the uneven structure on the side surface is Rs, these radii of curvature satisfy the following relational expression:
Rs>Rf2>Rf1>Rr2>Rr1
The solar cell according to claim 4 . A solar cell module in which the solar cells according to claim 1 or 2 are arranged in a two-dimensional manner. A method for producing a solar cell according to claim 1 or 2, comprising the steps of:
In the step of forming a concave-convex structure on the light-receiving surface side of the crystalline silicon substrate, a flow rate of the etching solution in at least a part of a peripheral portion of the light-receiving surface side is controlled to be faster than a flow rate of the etching solution in a central portion of the light-receiving surface side.
A method for manufacturing solar cells. a crystalline silicon substrate having an uneven structure on a light receiving surface side, a back surface side, and a side surface side;
a first conductive type semiconductor layer formed on the light receiving surface side or the back surface side of the substrate;
a second conductive type semiconductor layer formed on the light receiving surface side or the back surface side of the substrate;
a first electrode layer formed on the first conductive type semiconductor layer;
a second electrode layer formed on the second conductive type semiconductor layer;
A solar cell comprising:
In the substrate, a radius of curvature of a top portion of the concave-convex structure on the side surface is larger than a radius of curvature of a top portion of the concave-convex structure in a central portion of the light receiving surface side and a radius of curvature of a top portion of the concave-convex structure in a central portion of the back surface side.
Solar cell. The solar cell according to claim 8, wherein the radius of curvature of the top portion of at least a portion of the uneven structure in the peripheral portion of the light-receiving surface side of the substrate is greater than the radius of curvature of the top portion of the uneven structure in the center of the light-receiving surface side. In the substrate, if the radius of curvature of the top portion of the uneven structure on the side surface is Rs, the radius of curvature of the top portion of the uneven structure in the central portion on the light-receiving surface side is Rf1, and the radius of curvature of the top portion of at least a portion of the uneven structure in the peripheral portion on the light-receiving surface side is Rf2, these radii of curvature satisfy the following relational expression:
Rs>Rf2>Rf1
The solar cell according to claim 9 . The solar cell according to claim 8, wherein the radius of curvature of the top portion of the uneven structure of at least a portion of the peripheral portion of the back surface side of the substrate is greater than the radius of curvature of the top portion of the uneven structure of the central portion of the back surface side. In the substrate, when the radius of curvature of the top portion of the uneven structure on the side surface is Rs, the radius of curvature of the top portion of the uneven structure in the central portion of the back surface is Rr1, and the radius of curvature of the top portion of at least a portion of the uneven structure in the peripheral portion of the back surface is Rr2, these radii of curvature satisfy the following relational expression:
Rs>Rr2>Rr1
The solar cell according to claim 11. A method for producing a solar cell according to any one of claims 8 to 12, comprising the steps of:
In the step of forming a concave-convex structure on a light receiving surface side, a back surface side and a side surface of the crystalline silicon substrate,
controlling a flow rate of the etching solution in at least a part of the peripheral portion of the light-receiving surface side and in the side surface side to be faster than a flow rate of the etching solution in a central portion of the light-receiving surface side;
a flow rate of the etching solution on at least a part of the peripheral portion of the rear surface side and on the side surface is controlled to be faster than a flow rate of the etching solution on the central portion of the rear surface side;
A method for manufacturing solar cells.

Images