JP2014229826A - Manufacturing method of solar cell element and solar cell element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar cell element with improved power generation efficiency including a selective emitter formed by doping with boron on an N-type single crystal silicon substrate.SOLUTION: The solar cell element includes a selective emitter which is formed by doping with boron on an N-type single crystal silicon substrate. After disposing a diffusion agent at only a portion to form a high concentration doping layer, the solar cell element is subjected to thermal diffusion and etching with alkaline solution to obtain a selective emitter having a desired boron dopant concentration distribution and configuration.

Description

  The present invention relates to a solar cell element and a manufacturing method thereof.

  As one of solar cells, a selective emitter solar cell is known. A selective emitter solar cell is a solar cell in which a dopant concentration in a portion in contact with an electrode is made high in a light receiving surface of a semiconductor substrate included in the solar cell and a dopant concentration in a portion not in contact with the electrode is made low. A selective emitter solar cell is known as a solar cell capable of increasing efficiency.

  As a method of forming a selective emitter structure, when a diffusing agent containing a dopant is applied to the entire light-receiving surface of a substrate and the diffusing agent is dried by lamp heating through a mask, the degree of drying is partially changed to perform annealing. Has proposed a process of diffusing dopants in the light receiving surface to form regions having different dopant concentrations (for example, Patent Document 1).

  As another method for forming the selective emitter structure, after forming a doping layer on the entire light-receiving surface of the substrate, the dopant layer is removed to a certain depth by using a mask to remove a desired portion of the doping layer to a certain depth. There has been proposed a process for forming different regions (for example, Patent Document 2).

JP-A-6-252428 JP 2010-74134 A

  However, in the method for forming a selective emitter structure described in Patent Documents 1 and 2, a mask is used to form regions having different dopant concentrations. Therefore, it has been necessary to go through many processes such as film formation, patterning, and cleaning, and there is a problem that the number of processes increases. This invention solves this subject, and it aims at providing the manufacturing method of the solar cell element which can form a selective emitter structure with few man-hours, and the solar cell of high conversion efficiency.

  The method for manufacturing a solar cell element of the present invention includes a substrate composed of an N-type doping semiconductor, a low concentration P-type doping layer formed on the main surface of the substrate, and the low concentration P-type on the main surface of the substrate. A solar cell element comprising: a high-concentration P-type doping layer disposed adjacent to a doping layer and having a dopant concentration higher than that of the low-concentration P-type doping layer; and an electrode formed on the high-concentration P-type doping layer A method of forming a diffusing agent containing boron in a partial region of the main surface of the substrate, and diffusing the boron into the main surface by heat treatment to form the partial region in the partial surface of the substrate. Forming the high-concentration P-type doping layer and forming the low-concentration P-type doping layer in a region adjacent to the high-concentration P-type doping layer; and the high-concentration P-type doping layer and the low-concentration P in an alkaline solution. Type dopin And a step of etching the layer, and forming an electrode on the high-concentration P-type doping layer, a.

  The solar cell element of the present invention includes a substrate made of an N-type doping semiconductor, a low-concentration P-type doping layer formed on the main surface of the substrate, and the main surface adjacent to the low-concentration P-type doping layer. And a high-concentration P-type doping layer having a dopant concentration higher than that of the low-concentration P-type doping layer, and an electrode formed on the high-concentration P-type doping layer. In the solar cell element of the present invention, a plurality of first convex shapes are formed on the low-concentration P-type doping layer, and a plurality of second convex shapes are formed on the high-concentration P-type doping layer. The apex angle of the first convex shape is sharper than the apex angle of the two convex shapes.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide a solar cell element with few man-hours. In addition, it is possible to provide a solar cell element with improved photoelectric conversion efficiency. In particular, the manufacturing efficiency of a solar cell element having a P-type selective emitter layer including a single crystal silicon substrate is increased, and the photoelectric conversion efficiency is increased.

Schematic diagram showing the structure of the solar cell element of the present invention The schematic diagram which shows the preparation process of the solar cell element of this invention Graph showing the relationship between etching depth and boron concentration when silicon (100) surface is etched for a certain period of time with potassium hydroxide + pure water + propanol solution

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1. FIG. 1 is a schematic cross-sectional view of a solar cell element according to an embodiment. This solar cell element includes a substrate 101, a low concentration doping layer 104 and a high concentration doping layer 103 formed on one main surface of the substrate 101, a surface electrode 109 disposed on the high concentration doping layer 103, Have Furthermore, the solar cell element of the present embodiment has an arbitrary passivation film 106 and an antireflection film 108 formed on the low concentration doping layer 104.

The substrate 101 is a semiconductor substrate, and is usually a single crystal silicon substrate. Further, the substrate 101 is preferably doped. Specifically, the substrate 101 is doped with a conductivity type different from the conductivity types of the lightly doped layer 104 and the heavily doped layer 103. For example, when the conductivity type of the lightly doped layer 104 and the heavily doped layer 103 is P type, the substrate 101 is N type. The substrate 101 is typically an N-type single crystal silicon substrate. N-type single crystal silicon uses, for example, phosphorus as a dopant, and the dopant concentration is 7 × 10 ¹⁵ atoms / cm ³ .

  An uneven shape is formed on one main surface of the substrate 101 (the surface on which the low-concentration doping layer 104 and the high-concentration doping layer 103 are formed, also referred to as “light-receiving surface”). More specifically, an uneven shape (texture 102a) having a relatively obtuse shape at the apex and bottom is formed in a region where the high-concentration doping layer 103 is formed on the main surface of the substrate 101. On the other hand, in the region of the main surface of the substrate 101 where the low-concentration doping layer 104 is formed, a concavo-convex shape (texture 102b) having a relatively acute vertex and bottom is formed.

  As described above, the low concentration doping layer 104 and the high concentration doping layer 103 are formed on one main surface of the substrate 101. The lightly doped layer 104 and the heavily doped layer 103 are doped with a conductivity type different from the conductivity type of the substrate 101. Specifically, when the substrate 101 is N-type single crystal silicon, it is doped P-type, and more specifically, boron is doped.

The dopant concentration of the high concentration doping layer 103 is higher than the dopant concentration of the low concentration doping layer 104. For example, when the high-concentration doping layer 103 and the low-concentration doping layer 104 are doped with boron, the surface concentration of boron in the high-concentration doping layer 103 is about 1 × 10 ²⁰ atoms / cm ³ , and the low-concentration doping layer The peak concentration of 104 boron is 5 × 10 ¹⁸ to 1 × 10 ¹⁹ atoms / cm ³ .

  As described above, the high-concentration doping layer 103 and the low-concentration doping layer 104 formed on one main surface of the substrate 101 constitute a selective emitter structure.

  The high-concentration doping layer 103 is formed on the texture 102a of the substrate 101, and the low-concentration doping layer 104 is formed on the texture 102b of the substrate 101.

  Furthermore, the dopant concentration (for example, boron concentration) in the low-concentration doping layer 104 is not uniform in the in-plane direction of the main surface, and may have a concentration distribution. For example, among the low-concentration doping layers 104, the low-concentration doping layer 104 close to the high-concentration doping layer 103 may have a high dopant concentration, and may have a concentration distribution that monotonously decreases as the distance from the high-concentration doping layer 103 increases. Among the dopant concentrations of the low-concentration doping layer 104, the highest concentration (concentration in a region close to the high-concentration doping layer 103) is about the lowest concentration (concentration in the region farthest from the high-concentration doping layer 103). Can be doubled.

  A surface electrode 109 is disposed on the high concentration doping layer 103. The surface electrode 109 is an Ag thin film having a thickness of 100 nm, for example, and has a comb shape.

  In addition, a passivation film 106 that is a silicon thermal oxide film having a thickness of 100 nm and an antireflection film 108 that is a plasma CVD-silicon nitride film having a thickness of 80 nm are stacked on the lightly doped layer 104.

On the other hand, a doping layer 105 is formed on the other main surface of the substrate 101. The doping layer 105 is preferably doped with a conductivity type different from that of the lightly doped layer 104 and the heavily doped layer 103. That is, when the lightly doped layer 104 and the heavily doped layer 103 are doped P-type, the doped layer 105 is doped N-type, and is typically doped with phosphorus. The dopant concentration (for example, phosphorus concentration) in the doping layer 105 is 1 × 10 ²⁰ atoms / cm ³ .

  An uneven shape (texture 102c) may be formed on the other main surface of the substrate 101 (the surface on which the doping layer 105 is formed, also referred to as “back surface”). That is, the doping layer 105 is preferably formed on the texture 102c.

  Further, a back electrode 110 is disposed on the doping layer 105 doped with phosphorus. The back electrode 110 is an Ag thin film with a thickness of 100 nm, for example, and has a comb-teeth shape. A passivation film 107 is formed on the doping layer 105 in a region where the back electrode 110 is not disposed. The passivation film 107 is a silicon thermal oxide film having a thickness of 100 nm, for example.

2. Photoelectric Conversion of Solar Cell Element The low concentration doping layer 104 in the solar cell element of the embodiment is formed on the texture 102b, and the apex angle of the texture 102b is an acute angle. An object that blocks light such as the surface electrode 109 is not disposed in the lightly doped layer 104, and the lightly doped layer 104 is a region that takes in light from the outside. When the apex angle of the texture 102b of the lightly doped layer 104 is an acute angle, the light capturing effect is enhanced for the following reason.

  The light incident on the doping layers (103 and 104) from the light receiving surface is reflected by the texture and confined inside the doping layer. That is, the textured silicon substrate surface is more easily confined in the doping layer than the flat silicon substrate surface, and the light path passing through the doping layer can be lengthened.

  The texture 102a having a relatively round shape at the top and bottom in the solar cell element according to the embodiment is closer to a plane than the texture 102b having a relatively acute vertex and bottom. Therefore, the light incident on the substrate is easily reflected by the sharp texture 102b and is not easily reflected by the round texture 102a. Therefore, compared with the high-concentration doping layer 103, light is easily confined in the low-concentration doping layer 104, and the optical path inside the low-concentration doping layer 104 becomes long.

  On the other hand, the high-concentration doping layer 103 in the solar cell element of the embodiment is formed on the texture 102a, and the apex angle of the texture 102a is obtuse or rounded. Since the surface electrode 109 is formed on the high-concentration doping layer 103, the light directly incident on the high-concentration doping layer 103 from the outside is small, but the light incident on the low-concentration doping layer 104 is incident on the high-concentration doping layer 103. Can be incident.

  The high-concentration doping layer 103 containing a high-concentration dopant is easier to absorb light than the low-concentration doping layer 104. Therefore, it is preferable that the light path passing through the vicinity of the high concentration doping layer 103 is as short as possible.

  In order to shorten the path of light passing through the vicinity of the high-concentration doping layer 103, it is only necessary to make light reflection by the texture in the high-concentration doping layer 103 difficult (relatively easy to transmit). That is, it is preferable to suppress light reflection (reduce the number of reflections) by making the apex angle of the texture 102a on which the high-concentration doping layer 103 is formed an obtuse angle. In this way, light absorption by the high-concentration doping layer 103 can be reduced by relatively reducing light reflection at the texture 102a.

  Further, when the light receiving surface of the solar cell element is irradiated with light, a small number of carriers are generated in the low-concentration doping layer 104 and the underlying substrate region. When the generated minority carriers reach the surface electrode 109, electric power can be taken out.

  Minority carriers flow through a relatively low resistance portion. Therefore, many minority carriers flow in the vicinity of the surface whose resistance is reduced by doping. In addition, since minority carriers are collected by the surface electrode 109, the closer to the surface electrode 109, the larger the number. Therefore, in order to prevent the disappearance of minority carriers due to resistance loss, it is preferable that the resistance in the vicinity of the surface of the substrate 101 is lower as the surface electrode 109 is closer.

  In the solar cell element of the embodiment, the dopant concentration of the lightly doped layer 104 is increased as it is closer to the surface electrode 109, that is, the resistance is reduced. Therefore, the disappearance of minority carriers due to resistance loss can be suppressed.

  Furthermore, the apex angle of the texture 102a on which the high-concentration doping layer 103 in the present solar cell element is formed is obtuse or rounded. In order to make the apex angle of the texture 102a acute, the etching amount is increased (etching thickness is increased) as the distance from the apex is increased. As a result, the doping layer in the vicinity of the apex is thick, but the doping layer tends to become thinner as the distance from the apex increases. Carriers tend to concentrate in the thin portion of the doping layer, and the recombination rate increases. On the other hand, in order to make the apex angle of the texture 102a obtuse, the etching amount may be suppressed as a whole. As a result, the thickness of the doping layer is relatively uniform (generally thick). Therefore, carriers are less likely to concentrate and the recombination occurrence rate is less likely to increase.

  Thus, the photoelectric conversion efficiency of the solar cell element of the embodiment can be improved as a result of the improvement of the light capturing efficiency from the lightly doped layer 104, the suppression of the disappearance of carriers, and the reduction of the recombination probability.

3. About the manufacturing method of a solar cell element Fig.2 (a)-(i) has shown typically the cross section of a part of manufacturing intermediate body of a solar cell element, and shows the manufacturing method of the solar cell element which concerns on embodiment. Outline.

A substrate 201 made of silicon single crystal which is an N-type doping semiconductor is prepared (FIG. 2A). The substrate 201 is obtained by slicing an N-type silicon ingot. The method for producing the silicon ingot may be either the Czochralski (CZ) method or the floating zone (FZ) method. In this embodiment, a silicon ingot is obtained using the CS method. The dopant of silicon is preferably phosphorus, and the dopant concentration is preferably about 1 × 10 ^{15 to} 5 × 10 ¹⁶ atoms / cm ³ . The dopant concentration of the substrate 201 in this embodiment is 7 × 10 ¹⁵ atoms / cm ³ .

  Next, the substrate 201 is immersed in an aqueous solution of sodium hydroxide that is an alkaline solution, thereby removing a damaged layer due to the slicing of the substrate 201.

  Next, the substrate 201 is dipped in an aqueous solution obtained by adding isopropyl alcohol to an aqueous potassium hydroxide solution to form chevron-shaped textures 202 on both the front and back surfaces (main surface) of the substrate 201 (FIG. 2B). In the texture formation, if an etching region is defined using an etching mask, for example, a regular island-shaped region is defined, a periodic texture can be obtained. On the other hand, when the entire front and back surfaces of the substrate 201 are etched without using an etching mask, a random texture is obtained. In the present embodiment, the entire front and back surfaces of the substrate 201 are etched to form a random texture. The height of the convex portion of the texture was about 10 μm.

  Next, silicon oxide films 203 are formed on both surfaces of the substrate 201. The silicon oxide film 203 is formed by thermally oxidizing both surfaces of the substrate 201 by heating the substrate 201 in the atmosphere at 950 ° C. for 1 hour. Of the silicon oxide films formed on both surfaces of the substrate 201, the silicon oxide film on the back surface is removed using a chemical solution such as hydrofluoric acid to leave a silicon oxide film on the front surface (FIG. 2C). By the oxidation treatment, the peak of the mountain and the bottom of the valley of the texture 202 become obtuse and become the texture 202a.

  An N-type doping layer 204 is formed on the back surface by applying a coating agent containing phosphorus on the entire back surface of the substrate 201 from which the silicon oxide film has been removed, and performing a heat treatment at 950 ° C. for 30 minutes. At this time, a glass film is formed on the N-type doping layer 204. The formed glass film is removed by using a chemical solution such as hydrofluoric acid. At this time, the silicon oxide film 203 formed on the surface of the substrate 201 is also removed (FIG. 2D).

The surface dopant concentration of the N-type doping layer 204 is desirably about 1 × 10 ^{18 to} 5 × 10 ²⁰ atoms / cm ³ . In this embodiment, it is 1 × 10 ²⁰ atoms / cm ³ .

  Next, silicon oxide films 205 are formed on both surfaces of the substrate 201. Similar to the silicon oxide film 203, the silicon oxide film 205 is formed by thermally oxidizing both surfaces of the substrate 201 by heating the substrate 201 at 950 ° C. for 1 hour in the atmosphere. Of the silicon oxide films on both sides, the silicon oxide film on the front surface is removed using a chemical solution such as hydrofluoric acid to leave the silicon oxide film 205 on the back surface (FIG. 2E).

  A coating agent containing boron is applied to a desired portion of the surface of the substrate 201 using screen printing. Thereafter, heat treatment is performed at 950 ° C. for 1 hour. As a result, the high-concentration P-type doping layer 206 can be formed in a desired portion, and at the same time, the low-concentration P-type doping layer 207 is formed on the surface other than the high-concentration P-type doping layer 206 by autodoping. The dopant concentration in the low-concentration P-type doping layer 207 formed by auto-doping is lower as the region is farther from the high-concentration P-type doping layer 206.

  A glass film is formed on the high-concentration P-type doping layer 206 and the low-concentration P-type doping layer 207 by the heat treatment. The formed glass film is removed by using a chemical solution such as hydrofluoric acid (FIG. 2 (f)). At this time, the silicon oxide film 205 on the back surface is also removed.

  Further, a part in the thickness direction of the high-concentration P-type doping layer 206 and the low-concentration P-type doping layer 207 is etched with an alkali solution containing sodium hydroxide as a main component (FIG. 2G). In this embodiment, an ethylene glycol solution containing sodium hydroxide is used as the alkaline solution, but an alkaline solution such as a propanol solution containing potassium hydroxide, an aqueous tetramethylammonium hydroxide solution, or an isopropyl alcohol solution containing sodium carbonate is used. May be.

  FIG. 3 shows a mixed solution of pure water containing potassium hydroxide and propanol, when the (100) orientation plane of the substrate 201 made of a silicon single crystal having a doping layer doped with boron is etched for a certain period of time. It is a graph which shows the relationship between the boron concentration in the doping layer etched, and the etching depth of a doping layer. The etching rate during the etching process is substantially constant. As shown in FIG. 3, the etching rate of the doping layer by the alkaline solution decreases as the dopant concentration increases.

  Therefore, when the high-concentration P-type doping layer 206 and the low-concentration P-type doping layer 207 are simultaneously etched with an alkaline solution, the low-concentration P-type doping layer 207 is selectively etched, and the high-concentration P-type doping layer 206 is Difficult to etch. Therefore, it is not necessary to mask the high concentration P-type doping layer 206 with a resist or the like, and the number of steps for etching can be reduced.

  The dopant concentration of the low-concentration P-type doping layer 207 can be controlled by etching with an alkaline solution. Since the dopant is diffused from the substrate surface, the dopant concentration of the low-concentration P-type doping layer 207 is higher as it is closer to the surface. Therefore, the surface dopant concentration of the low-concentration P-type doping layer 207 decreases as the etching thickness of the low-concentration P-type doping layer 207 increases. Therefore, the surface dopant concentration of the low-concentration P-type doping layer 207 can be controlled by the etching depth.

The surface dopant concentration of the high concentration P-type doping layer 206 is preferably about 5 × 10 ^{19 to} 5 × 10 ²⁰ atoms / cm ³ , and the surface dopant concentration of the low concentration P-type doping layer 207 is 1 × 10 ¹⁷ to 1 × 10. ^{About 19} atoms / cm ³ is desirable. In the present embodiment, the surface dopant concentration of the high-concentration P-type doping layer 206 is about 1 × 10 ²⁰ atoms / cm ³ , and the surface dopant concentration of the low-concentration P-type doping layer 207 is 5 × 10 ¹⁸ to 1 × 10 ¹⁹ atoms. / Cm ³ or so.

  Further, selective etching with respect to the plane orientation of the single crystal silicon substrate is performed by etching with an alkaline solution, and the obtuse texture 202a can be changed to an acute texture 202b (FIG. 2 (g)). The shape of the top and bottom of the texture 202 at the stage shown in FIG. 2B is acute; however, the top and bottom of the texture 202a at the stage shown in FIG. Due to a heat treatment process such as thermal oxidation, and a cleaning process such as oxide film removal, it becomes obtuse or rounded. On the other hand, the shape of the top and bottom of the texture 202b at the stage shown in FIG.

  Furthermore, a step is generated between the high concentration P-type doping layer 206 and the low concentration P-type doping layer 207 by etching with an alkaline solution. That is, the apex height of the high concentration P-type doping layer 206 is higher than the apex of the texture of the low concentration P-type doping layer 207.

  Next, the end surface of the substrate 201 is etched by about 3 μm with a plasma etcher, and wet cleaning is performed to perform PN junction separation (not shown).

Next, a surface passivation film 208 (film thickness: 100 nm) made of Al ₂ O _{3 is formed} by atomic layer deposition. Further, a back surface passivation film 209 (film thickness: 100 nm) which is a silicon oxide film is formed on the back surface by thermal oxidation at 950 ° C. for 10 minutes. Further, an antireflection film 210 (film thickness: about 80 nm), which is a silicon nitride film, is laminated on the surface of the substrate 201 (on the surface passivation film 208) by plasma CVD (FIG. 2 (h)).

  Next, paste is applied to the N-type doping layer 204 and the high-concentration P-type doping layer 206 in a comb-teeth shape using screen printing and dried. The paste is composed mainly of, for example, silver and glass frit or the like is mixed. Since the high-concentration P-type doping layer 206 has a step with respect to the low-concentration P-type doping layer 207, the paste can be applied to the high-concentration P-type doping layer 206 with high positional accuracy by screen printing.

  Finally, baking is performed at 800 ° C. for 20 minutes in a baking furnace to form a front electrode 211 and a back electrode 212 that are electrically connected to the N-type doping layer 204 and the high-concentration P-type doping layer 206, respectively (FIG. 2 (i)).

  Thus, it becomes possible to form a solar cell element efficiently.

  In the method for manufacturing a solar cell element of the present invention, the number of manufacturing steps can be reduced by performing etching without a mask. Further, since the characteristic is that the etching rate with an alkaline solution is faster as the doping concentration is lower, the low concentration doping layer can be selectively etched.

  Moreover, in the manufacturing method of the solar cell element of this invention, a level | step difference can be provided between a low concentration doping layer and a high concentration doping layer. If this step is utilized, alignment in the film formation of the electrode becomes easy, and the surface electrode 211 with a narrow pitch can be formed with high reliability.

  Furthermore, the apex angle of the texture (unevenness) formed on the substrate 201 is not an acute angle (sharp) as in the initial formation (FIG. 2B), but an obtuse angle (blunt) or It becomes round (FIG. 2 (f)). In this embodiment, since the low-concentration P-type doping layer 207 is etched with an alkaline solution, the apex angle of the texture of the low-concentration P-type doping layer 207 can be returned to an acute angle. This is because the alkali etching rate varies depending on the plane orientation of the silicon substrate.

  The solar cell element and the manufacturing method thereof according to the present invention can improve the conversion efficiency while avoiding an increase in cost as compared with the prior art, and can be applied to applications in the energy field such as solar power generation.

DESCRIPTION OF SYMBOLS 101 Substrate 102a-c Texture 103 High concentration doping layer 104 Low concentration doping layer 105 Doping layer 106, 107 Passivation film 108 Antireflection film 109 Front surface electrode 110 Back surface electrode 201 Substrate 202, 202a, 202b Texture 203 Silicon oxide film 204 N-type doping Layer 205 Silicon oxide film 206 High-concentration P-type doping layer 207 Low-concentration P-type doping layer 208 Surface passivation film 209 Back surface passivation film 210 Antireflection film 211 Surface electrode 212 Back surface electrode

Claims (7)

A substrate composed of an N-type doping semiconductor; a low-concentration P-type doping layer formed on the main surface of the substrate; and a main surface of the substrate adjacent to the low-concentration P-type doping layer. A method for manufacturing a solar cell element, comprising: a high concentration P-type doping layer having a dopant concentration higher than that of the concentration P-type doping layer; and an electrode formed on the high concentration P-type doping layer.
Forming a diffusion agent containing boron on a partial region of the main surface of the substrate;
The boron is diffused into the main surface by heat treatment to form the high-concentration P-type doping layer in the partial region, and the low-concentration P-type doping layer is formed in a region adjacent to the high-concentration P-type doping layer. Forming, and
Etching the high-concentration P-type doping layer and the low-concentration P-type doping layer with an alkaline solution;
Forming an electrode on the high-concentration P-type doping layer;
The manufacturing method of the solar cell element characterized by including.   The method for manufacturing a solar cell element according to claim 1, wherein the etching is performed without masking the high-concentration P-type doping layer.   The method for manufacturing a solar cell element according to claim 1, wherein the heat treatment is performed while holding the substrate in a nitrogen atmosphere.   4. The solar cell element according to claim 1, wherein the alkaline solution contains at least one component of sodium hydroxide, potassium hydroxide, sodium carbonate, and tetramethylammonium hydroxide (TMAH). 5. Production method. A substrate composed of an N-type doped semiconductor; a low-concentration P-type doping layer formed on a main surface of the substrate; and a main surface of the substrate adjacent to the low-concentration P-type doping layer, the low-concentration P A high concentration P-type doping layer having a higher dopant concentration than the type doping layer, and an electrode formed on the high concentration P-type doping layer,
A plurality of first convex shapes are formed on the low-concentration P-type doping layer, a plurality of second convex shapes are formed on the high-concentration P-type doping layer, and the first convex shape is greater than the apex angle of the second convex shape. A solar cell element in which the apex angle of one convex shape is sharper.   The solar cell element according to claim 5, wherein the low-concentration P-type doping layer and the high-concentration P-type doping layer contain boron as a dopant. 7. The solar cell element according to claim 5, wherein the dopant concentration in the low-concentration P-type doping layer gradually increases as it approaches the high-concentration P-type doping layer.

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