KR101122048B1

KR101122048B1 - Solar cell and method for manufacturing the same

Info

Publication number: KR101122048B1
Application number: KR1020090017736A
Authority: KR
Inventors: 김선영; 김철; 최영호
Original assignee: 엘지전자 주식회사
Priority date: 2009-03-02
Filing date: 2009-03-02
Publication date: 2012-03-12
Also published as: KR20100098992A

Abstract

The present invention relates to a solar cell, wherein the solar cell includes a substrate, a semiconductor layer formed on the substrate, a protective film formed on the semiconductor layer, and an opening formed in the protective film to expose a portion of the semiconductor layer, the opening at least Two straight portions and at least two rounded corners connected to the straight portions. For this reason, the uniformity of the formed opening part improves, and the operation efficiency of the electrode, terminal, etc. formed in each opening part improves, for this reason, the operation efficiency of a solar cell also improves.

Solar cell, opening, back contact, screen printing, contact hole

Description

SOLAR CELL AND METHOD FOR MANUFACTURING THEREOF {SOLAR CELL AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a solar cell and a method of manufacturing the same.

Recently, as the prediction of depletion of existing energy sources such as oil and coal is increasing, interest in alternative energy to replace them is increasing. Among them, solar cells generate electrical energy from solar energy, which is advantageous in that the environmentally friendly and energy source of solar energy is infinite and its life is long.

Solar cells are largely classified into silicon solar cells, compound semiconductor solar cells, and tandem solar cells according to raw materials, and silicon solar cells are the mainstream.

A typical silicon solar cell includes a substrate and an emitter layer made of semiconductors having different conductive types such as p-type and n-type, and electrodes formed on the substrate and the emitter, respectively. At this time, p-n junction is formed in the interface of a board | substrate and an emitter part.

In contrast, the solar cell may have a back junction electrode type structure in which all of the electrodes serving as the conductive transparent electrode layer and the back electrode are formed on the semiconductor substrate to which light is not incident. The solar cell of such a back electrode type structure increases the area to which light is incident, thereby improving the efficiency of the solar cell.

When solar light is incident on the solar cell, electrons and holes are generated in a semiconductor doped with an n-type or p-type impurity by a photovoltaic effect. The electrons and holes generated by the photovoltaic effect are attracted to the n-type emitter and p-type substrate, respectively, and are collected by electrodes electrically connected to the substrate and the emitter, respectively. .

The technical problem to be achieved by the present invention is to improve the transmission efficiency of the solar cell.

Another technical problem to be achieved by the present invention is to improve the efficiency of a solar cell.

A solar cell according to an aspect of the present invention includes a substrate, a semiconductor layer formed on the substrate, a protective film formed on the semiconductor layer, and an opening formed in the protective film to expose a portion of the semiconductor layer, the openings being at least two A straight portion and at least two rounded corners connected to the straight portion are provided.

The openings may have the same length or may have different sides facing each other.

The length ratio of two curved portions of the at least two curved portions connected to one straight portion of the at least two straight portions and the one straight portion may be 1: 49.5: 49.5 to 98: 1: 1.

The opening may have a polygonal structure having a curved edge.

The substrate may be a semiconductor substrate. In addition, the substrate may be a glass substrate or a plastic substrate.

The solar cell according to the above feature may further include an electrode contacting the semiconductor layer exposed through the opening.

Preferably, the semiconductor layer and the substrate have opposite conductivity types.

According to another aspect of the present invention, there is provided a method of manufacturing a solar cell, including preparing a semiconductor substrate having a first conductivity type, and forming a semiconductor layer having a second conductivity type opposite to the first conductivity type on the semiconductor substrate. Forming a protective film on the semiconductor layer, applying an etching paste on the protective film to form an opening that exposes a portion of the semiconductor layer, and forming an electrode in contact with the semiconductor layer exposed through the opening And the opening has at least two straight edges and at least two rounded corners connected to the straight portions.

According to the characteristic of this invention, the uniformity of the formed opening part improves, the operation efficiency of the electrode, the terminal, etc. formed in each opening part improves, and, thereby, the operation efficiency of a solar cell also improves.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification. When a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the case directly above another portion but also the case where there is another portion in between. On the contrary, when a part is "just above" another part, there is no other part in the middle. Also, when a part is formed as "whole" on the other part, it means not only that it is formed on the entire surface (or the front surface) of the other part but also not on the edge part.

With reference to the drawings will be described the shape of the opening formed in the film according to an embodiment of the present invention.

1 is a schematic view of an opening formed in a film according to an embodiment of the present invention, Figure 2 is a cross-sectional view taken along the line II-II in FIG.

In the present embodiment, the panels shown in Figs. 1 and 2 are formed by contacting each other with semiconductors doped with impurities of different conductivity types to form pn junctions, and forming electrodes by stacking films and the like on different types of semiconductors. It can be used as a panel for solar cells to produce electric power, but is not limited thereto.

In such a panel, the film 20 formed on the substrate 10 has an opening 81 having a polygonal shape or a cylindrical shape, for example, a rectangular shape with rounded corners. In this case, the substrate 10 may be a transparent substrate such as glass, a flexible substrate such as plastic, or a semiconductor substrate made of silicon or the like.

Each opening 81 has at least two straight portions and at least two curved portions connecting the two straight portions. At this time, the number of straight portions and the number of curved portions are the same. The length ratio of one straight portion and the two curved portions connected to the straight portion may be about 1: 49.5: 49.5 to about 98: 1: 1.

The opening 81 removes a portion of the one or more films 20 when the one or more films 20 are successively stacked on the substrate 10, so that the openings 81 may be formed on the substrate 10 or another film under the film 20. As a hole exposing a part, when the desired material is applied or laminated to the opening 81, the applied or laminated material functions as a terminal, a connecting member or an electrode, or the like, which contacts a part of the exposed substrate 10 or another film, or the substrate ( 10) or as an exposing port that exposes parts of other membranes.

In the solar cell, the opening 81 forms a plurality of electrodes respectively formed in the emitter portion and the substrate, or removes a portion of the emitter portion, thereby changing the doping concentration of impurities according to the position of the emitter portion. It is used to manufacture a battery or the like. However, the present invention is not limited thereto, and the openings 81 according to the present embodiment correspond to all of the holes formed when a part of the solar cell or the film of another kind is removed.

First, a method of forming a film 20 having an opening 81 on the substrate 10 will be described with reference to FIGS. 3A to 3C and 4 to 6.

3A to 3C are diagrams sequentially illustrating a film manufacturing method according to an embodiment of the present invention. 4 is a plan view of a screen mask according to an embodiment of the present invention, Figure 5 is a plan view of a screen mask according to the prior art. 6 is a cross-sectional view of a substrate on which a paste is printed on a film by a screen mask according to another embodiment of the present invention.

The film 20 is formed on the substrate 110. In this case, the film 20 may be an insulating film or a conductive film, and is formed through various film lamination methods such as sputtering, chemical vapor deposition, inkjet printing, and the like.

Next, as shown in FIG. 3B, the screen mask 800 for screen printing is aligned on the laminated film 20.

As shown in FIG. 4, the screen mask 800 includes a mesh net 801, a pattern forming unit 802 positioned on the mesh net 801, and a frame 803 for fixing the mesh net 801. Equipped.

Mesh net 801 is a thread of the specified thickness 804 is woven in the form of a net, the size of the opening (opening) formed between the yarn 804 and the yarn 804 is present in the thickness, unit area of the yarn 804 It varies depending on the number of meshes, the pattern shape and pattern size of the pattern forming unit 802.

The pattern formed in the pattern forming unit 802 has a polygon, for example, a quadrangular shape 80 having a rounded corner A1, as shown in FIG. That is, the quadrangular shape 80 having rounded corners A1 includes at least two straight portions and at least two curved portions connecting the two straight portions. At this time, the number of straight portions and the number of curved portions are the same. The length ratio of one straight portion and the two curved portions connected to the straight portion may be about 1: 49.5: 49.5 to about 98: 1: 1.

This pattern is completed by applying an emulsion to the mesh net 801 and hardening, and then removing the emulsion present in the rectangular region having rounded corners A1 using a pattern mask (not shown).

Next, when the etching paste 90 is pushed on the screen mask 800 using a squeeze 810, an etching having a shape such as a square shape 80 having a rounded corner A1 formed in the pattern forming unit 802 may be performed. A paste 90 is applied over the film 20 (FIG. 3C).

Next, the film 20 of the corresponding portion is removed by the etching paste 90 to form an opening 81 in the portion where the etching paste 90 is applied (FIG. 2). In this case, the shape of the opening 81 may also have a rectangular shape having rounded corners, such as a pattern shape formed in the pattern forming unit 802.

As such, in order to form the openings 81, as the screen mask 800 has a rectangular pattern having rounded corners A1, the shape of the openings 81 formed in the film 20 may also have rounded corners. It has a rectangular shape which has it, and the uniformity of the opening part 810 is improved.

As shown in FIG. 5, when the screen mask 800 has a pattern of square shape 81 having angled edges A2, a part of the opening formed in the angled edge portion A2 is covered by an emulsion, The opening size of the angled corner portion is not constant and the opening size of the angled corner portion is reduced. For this reason, the shape of the etching paste printed at the corners of the angled corners A2 is also not uniform, and the passage of the etching paste 90 is not made smoothly, thereby causing a portion where the etching paste 90 is not printed. In addition, the etch paste 90 pushed and printed by the squeegee 810 does not move to the end of the angular edge, so that the shape of the etch paste printed on the film 20 does not have the angular edge shape.

This causes a problem that the shape of the printed etching paste is not constant. As a result, when the pattern forming unit 801 of the screen mask 800 has a rectangular pattern having angled corners, there are many difficulties in implementing the angled corner shapes, and the etching paste 90 printed on the film 20 is formed. There arises a problem that the shape of?

In addition, when the pattern shape portion 801 of the screen mask 800 has a pattern of round shape 82 having no straight portion, the region of the corner portion A2 is excluded from the pattern formation region, so that the pattern formation region is an edge. The spacing of the yarns may be narrower than that of the polygonal shape (eg, squares) having a shape. As a result, the size of the opening is reduced, so that the portion where the etch paste does not pass in the middle of the round pattern 82 is difficult to form, thus making it difficult to form the round opening.

However, since the pattern forming unit 801 of the screen mask 800 according to the present exemplary embodiment has a polygonal pattern, for example, a quadrangular pattern having a rounded corner A1 having a curved corner portion of the curved edge portion, Since the size of the covered opening is reduced, the number of openings is reduced, and the angled corner portions, which are portions where the etching paste is difficult to penetrate, are removed, so that the printing operation of the etching paste 90 is smoothed. As a result, all of the shapes of the etching paste 90 printed on the film 20 have polygonal shapes with rounded corners, thereby improving the uniformity of the formation of the etching paste 90 printed on the film 90.

In the present exemplary embodiment, the pattern forming unit 802 of the screen mask 800 has a structure in which the mesh agent 801 is exposed by removing an oil applied to a quadrangular portion having rounded corners. However, as shown in FIG. 6, in an alternative embodiment the emulsion present in the mesh network 801 of the other portions, leaving the emulsion present in the mesh network 801 of the rectangular-shaped portion with rounded corners as opposed to FIG. 4. Has a structure removed. In this case, the paste 91 printed on the film 20 functions as an etch stop film that prevents the film 20 below it from being etched.

In addition, in the present embodiment, the description has been made based on the fact that the pattern forming portion 802 and the opening 81 have a rectangular shape having rounded corners. However, as described above, the pattern forming unit 802 and the opening 81 are not limited thereto, and the pattern forming unit 802 and the opening 81 include at least two curved portions connecting at least two straight portions and two straight portions, such as triangles and pentagons having rounded corners. Applicable to all polygonal and cylindrical shapes. In addition, the shape of the pattern forming unit 802 and the opening 81 may be the same length or different sides of the sides facing each other.

Moreover, although the screen printing method is used for the polygonal or cylindrical openings 81 having rounded corners in the present embodiment, the present invention is not limited thereto, and is different from the gravure printing method or the inkjet printing method. It can be formed using.

Next, referring to FIGS. 7 and 8, a solar cell employing a polygonal opening having rounded corners according to an embodiment of the present invention will be described.

7 is a partial cross-sectional view of a solar cell according to an exemplary embodiment of the present invention, and FIG. 8 is a plan view of an opening formed in a rear protective film of the solar cell shown in FIG. 7.

Referring to FIG. 7, a solar cell 1 according to an exemplary embodiment of the present invention may include a first substrate positioned on a substrate 110 and a substrate 110 (hereinafter, referred to as a “front portion”) in a direction in which light is incident. A protective passivation layer (front passivation layer) 120, an anti-reflection film 130 located on the front passivation layer 120, the substrate 110 facing the front portion without light incident (hereinafter referred to as a 'rear portion' The first impurity portion 141 positioned at the “and” second impurity portion 142 and the first impurity portion 141 spaced apart from the first impurity portion 141 at the rear surface of the substrate 110. Located on the second impurity portion 142, a rear passivation layer 150, which is a second passivation layer exposing a portion of the first and second impurity portions 141 and 142, and on the exposed first impurity portion 141. A plurality of first electrodes 161 positioned, a plurality of second electrodes 162 positioned on the exposed second impurity portion 142, and a front surface formed between the substrate 110 and the front passivation layer 120; And a (front surface field, FSF) section 170.

The substrate 110 is made of a semiconductor such as monocrystalline silicon or polycrystalline silicon having a n-type conductivity by doping with a first conductivity type, for example, n-type impurities. When the substrate 110 has an n-type conductivity type, the substrate 110 contains impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb). Alternatively, the substrate 110 may have a p-type conductivity type, and in this case, the substrate 110 may contain impurities of trivalent elements such as boron (B), gallium, indium, and the like. In addition, the substrate 110 may be made of a semiconductor material other than silicon.

The substrate 110 may also be textured to have a texturing surface with a plurality of irregularities. At this time, the texturing surface of the substrate 110 has a random pyramid shape or as a porous surface to realize a plurality of uneven structures. When the substrate 110 is made of monocrystalline silicon, texturing is performed using a base compound such as NaOH or KOG, and when the substrate 110 is made of polycrystalline silicon, such as nitric acid (HNO ₃ ) and hydrofluoric acid (HF) Texturing can be done by mixing the acid groups.

The front electric field unit 170 is positioned on the front surface of the substrate 110.

The front electric field unit 170 is formed by implanting impurities of the same conductivity type as the substrate 110, for example, n-type impurities, into the substrate 110 at a concentration higher than that of the substrate 110. Due to the impurity concentration difference with the substrate 110 due to the front electric field unit 170, a potential barrier is formed, and the movement of holes is prevented by the potential barrier. Thus, electrons and holes separated near the front portion of the substrate 110 are prevented from being recombined and lost.

The front passivation layer 120 is formed on the front electric field unit 170.

The front passivation layer 120 is made of silicon oxide (SiO ₂ ) or the like to reduce contact resistance between the lower layer and the upper layer, thereby preventing recombination of electrons and holes.

An antireflection film 130 made of silicon nitride (SiNx), titanium dioxide (TiO ₂ ), or the like is formed on the front passivation layer 120. When the anti-reflection film 130 is made of silicon nitride (SiNx), the front passivation layer 120 under the anti-reflection film 130 may be omitted.

The anti-reflection film 130 formed on the front passivation layer 120 reduces the reflectance of incident sunlight and increases the selectivity of a specific wavelength region, thereby increasing the efficiency of the solar cell. The front passivation layer 120 may have a thickness of about 70 nm to about 80 nm.

The first impurity portion 141 and the second impurity portion 142 are alternately formed on the rear surface of the substrate 110.

An impurity having a first conductivity type, for example, an n-type impurity, is doped in the first impurity portion 141 to a concentration higher than that of the substrate 110. At this time, the first impurity portion 141 functions as a back surface field (BSF) portion similar to the front field portion 170, thereby preventing electrons and holes from recombining and disappearing from the surface of the substrate 110. .

The second impurity portion 142 is doped with a high concentration of impurities having a second conductivity type opposite to the first conductivity type, for example, p-type impurities, so that the second impurity portion 142 is formed of an n-type substrate ( 110) and functions as an emitter portion forming a pn junction. Electron-hole pairs, which are charges generated as light enters the substrate 110 of the semiconductor, are separated into electrons and holes by built-in potential differences due to pn junctions. Moves toward p-type. Therefore, when the substrate 110 is n-type and the second impurity portion 142 is p-type, the separated electrons move to the first impurity portion 141 through the substrate 110 and the separated holes are the second impurity portion. Go to (142).

The back passivation layer 150 is formed on the first impurity portion 141 and the second impurity portion 142.

The back passivation layer 150 includes a plurality of first openings 181 exposing a part of the first impurity part 141 and a plurality of second openings 182 exposing a part of the second impurity part 142. As illustrated in FIG. 8, the first and second openings 181 and 182 have a polygonal shape such as a quadrangle having rounded corners.

The back passivation layer 150 is formed of silicon oxide (SiO ₂ ), silicon nitride (SiNx), or a combination thereof, and may have a thickness of about 300 nm or more. The rear protective layer 150 prevents carriers separated by electrons and holes from recombining and reflects the incident light into the solar cell so that the incident light is not lost to the outside, thereby reducing the amount of light lost to the outside.

In the present exemplary embodiment, the rear passivation layer 150 is formed as a single layer, but may have a multilayer structure such as a double layer or a triple layer.

The first electrode 161 is formed on the first impurity portion 141 exposed through the first opening 181 and the rear passivation layer 150 around the first opening 181, and the second opening 182 is formed. The second electrode 162 is formed on the second impurity portion 142 and the rear passivation layer 150 around the second opening 182.

The first electrode 161 is electrically connected to the first impurity portion 141, and the second electrode 162 is electrically connected to the second impurity portion 142.

The first and second electrodes 161 and 162 extend parallel to each other in one direction at a predetermined interval, and carry carriers such as electrons and holes that move toward the first impurity portion 141 and the second impurity portion 142. Collect it and move it to an external device.

As described above, since a portion of the first and second electrodes 161 and 162 overlap a portion of the rear passivation layer 150 to include a wide end portion, the contact resistance is reduced when the external driving circuit is connected to the contact efficiency. Is higher.

The first and second electrodes 161 and 162 are made of at least one conductive metal material, and examples of the conductive metal materials are nickel (Ni), copper (Cu), silver (Ag), aluminum (Al), and tin. (Sn), zinc (Zn), indium (In), titanium (Ti), gold (Au) and at least one selected from the group consisting of a combination thereof, but may be made of other conductive metal materials other than.

For example, the first and second electrodes 161 and 162 may include a conductive paste including a conductive metal material such as aluminum (Al) in silver (Ag) through screen printing to form the first and second openings 181,. 182 and its surroundings.

In the present embodiment, since the first and second openings 181 and 182 formed in the rear passivation layer 150 have a polygonal shape having rounded corners with excellent uniformity, the shape of the openings 181 and 182 is based on the shape of the openings 181 and 182. The uniformity of the shapes of the first electrode 161 and the second electrode 162 formed on the openings 181 and 182 is also improved. In addition, the first and second openings 181 and 182 do not have angled corner portions in which conductive paste is difficult to penetrate, and thus, the first and second electrodes 161 formed on the first and second openings 181 and 182. The uniformity of the shape is further improved, and the contact force of the first and second electrodes 161 and 162 in the first and second openings 181 and 182 is also improved. Therefore, the uniformity and contact force of the first and second electrodes 161 and 162 are improved due to the first and second openings 181 and 182, so that the transmission efficiency of the first and second electrodes 161 and 162 is improved. The operation uniformity between the electrodes 161 and 162 is improved and the operation efficiency of the first and second electrodes 161 and 162 is increased.

In the present embodiment, the first and second electrodes 161 and 162 are formed using screen printing, but alternatively, chemical vapor deposition such as plasma enhanced chemical vapor deposition (PECVD) is performed. It can be formed through various methods such as deposition, CVD.

In the solar cell according to the present exemplary embodiment having the structure as described above, the first electrode 161 and the second electrode 162 are positioned on the rear surface of the substrate 110 to which light is not incident, thereby increasing the area of the incident light. As a back contact solar cell, its operation is as follows.

When light is irradiated to the solar cell 1 and incident to the substrate 110 of the semiconductor through the anti-reflection film 130 and the front passivation layer 120, electron-hole pairs are generated in the substrate 110 of the semiconductor by light energy. In this case, the reflection loss of the light incident on the substrate 110 by the anti-reflection film 130 is reduced, so that the amount of light incident on the substrate 110 is further increased.

These electron-hole pairs are separated from each other by the pn junction of the substrate 110 and the second impurity portion 142 so that the electrons move toward the first impurity portion 141 having an n-type conductivity type, and the holes are p-type. It moves toward the second impurity portion 142 having a conductivity type of. As such, the electrons moved toward the first impurity portion 141 are collected by the first electrode 161 and output to the external device, and the holes moved toward the second impurity portion 142 are moved by the second electrode 162. Is collected and output to an external device.

At this time, the contact force and the transmission efficiency of the first and second electrodes 161 and 162 are increased by the first and second openings 181 and 182 having rounded corners, thereby improving the operating efficiency of the solar cell 1. .

As shown in FIGS. 7 and 8, the solar cell having the openings 181 and 182 according to the embodiment of the present invention has both the first and second electrodes 161 and 162 at the rear surface of the substrate 110. An example is a back contact solar cell located.

However, as an alternative example of the solar cell having an opening according to an embodiment of the present invention, a solar cell in which an electrode collecting electrons and an electrode collecting holes are formed on the front and rear surfaces of the substrate, respectively. In this case, the opening is formed in the antireflection film formed on the emitter portion forming a pn junction with the substrate to lower the reflectance of light and also serve as a protective film to protect the underlying layer, so as to contact the emitter portion formed on the substrate and the electrode. Is used.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

1 is a schematic diagram of an opening formed in a film according to an embodiment of the present invention.

2 is a cross-sectional view taken along the line II-II of FIG. 1.

3A to 3C are diagrams sequentially illustrating a film manufacturing method according to an embodiment of the present invention.

4 is a plan view of a screen mask according to an embodiment of the present invention.

5 is a plan view of a screen mask according to the prior art.

6 is a cross-sectional view of a substrate on which a paste is printed on a film by a screen mask according to another embodiment of the present invention.

7 is a partial cross-sectional view of a solar cell according to an embodiment of the present invention.

8 is a plan view of an opening formed in a rear protective film of the solar cell shown in FIG. 7.

* Description of the Drawing Symbols *

10, 110: substrate 120: front protective film

130: antireflection film 141: first impurity portion

142: second impurity portion 150: rear protective film

161: first electrode 162: second electrode

170: front field portion 81, 181, 182: opening

Claims

Board,

A semiconductor layer formed on the substrate,

A protective film formed on the semiconductor layer, and

An opening formed in the passivation layer to expose a portion of the semiconductor layer,

And the opening has at least two straight portions and at least two curved portions connected to the straight portions.

In claim 1,

The opening is a solar cell having the same length of the side facing each other.

In claim 1,

The opening of the solar cell is different in the length of the side facing each other.

The method of claim 2 or 3,

The length ratio of two curved portions of the at least two curved portions connected to one of the at least two straight portions and the one straight portion is from 1: 49.5: 49.5 to 98: 1: 1.

In claim 1,

The opening has a polygonal structure having a curved corner.

In claim 1,

The substrate is a solar cell.

In claim 1,

The substrate is a glass substrate or a plastic substrate.

In claim 1,

And a electrode in contact with the semiconductor layer exposed through the opening.

In claim 1,

And the semiconductor layer and the substrate have opposite conductivity types.

Preparing a semiconductor substrate having a first conductivity type,

Forming a semiconductor layer on the semiconductor substrate, the semiconductor layer having a second conductivity type opposite to the first conductivity type,

Forming a protective film on the semiconductor layer;

Applying an etching paste on the protective film to form an opening that exposes a portion of the semiconductor layer, and

Forming an electrode in contact with the semiconductor layer exposed through the opening,

The opening has at least two straight portions and at least two curved portions connected to the straight portions.

Method for manufacturing a solar cell.