JP2005252210A - Solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell which enables obtaining high photoelectric conversion efficiency, irrespective of the size of the incident angle with respect to the solar battery. <P>SOLUTION: This solar cell 1 comprises a first conductivity-type semiconductor substrate 5 having a plurality of pillar-shaped convex portions 3 on the front surface. On a side surface portion 3a and the top surface portion 3b of the pillar-shaped convex portion 3 and on each surface region 5a between the pillar-shaped convex portions 3 adjacent to each other, a second conductivity-type semiconductor layer is formed.In this solar battery 1, incident light can have a plurality of chances of being absorbed by the solar battery 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solar cell.

One way to improve the efficiency of the solar cell is to reduce the reflectivity at the surface of the solar cell. As a method for reducing the reflectance on the surface, a method of forming irregularities on the surface is known (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 2003-69061

  Light enters a solar cell at various incident angles, and generally, the greater the incident angle, the higher the reflectance on the surface of the solar cell, and as a result, the photoelectric conversion efficiency decreases. The same applies to a solar cell having irregularities on the surface.

This invention is made | formed in view of the situation which concerns, and provides the solar cell from which high photoelectric conversion efficiency is obtained irrespective of the magnitude | size of the incident angle to a solar cell.

  The solar cell of the present invention includes a first conductivity type semiconductor substrate having a plurality of columnar convex portions on the surface, and each surface between the side surface portion and the upper surface portion of the columnar convex portion and two adjacent columnar convex portions. A second conductivity type semiconductor layer is formed in the region.

  Incident light to the side surface portion of the columnar convex portion is absorbed by the side surface portion of the columnar convex portion or reflected by the surface of the side surface portion. The reflected light travels to each surface region between two adjacent columnar convex portions. Light directed to each surface area is either absorbed in that area or reflected at the surface of that area. The reflected light travels again to the side surface of the columnar convex portion.

  Thus, in the solar cell of the present invention, incident light can have multiple opportunities to be absorbed by the solar cell. Therefore, in the solar cell of the present invention, incident light can be used effectively, and as a result, high photoelectric conversion efficiency can be obtained.

  Moreover, in the conventional solar cell, when the incident angle to the solar cell is a large value such as 70 ° or more, the reflectance on the surface of the solar cell is increased, and the photoelectric conversion efficiency is lowered. On the other hand, in the solar cell of the present invention, even when the incident angle to the solar cell is large, the incident angle to the side surface portion of the columnar convex portion is small. As a result, the reflectance on the solar cell surface can be reduced. it can.

  That is, according to the solar cell of the present invention, high photoelectric conversion efficiency can be obtained regardless of the incident angle to the solar cell.

1. First Embodiment A solar cell according to a first embodiment of the present invention includes a first conductivity type semiconductor substrate having a plurality of columnar convex portions on a surface thereof, and a side surface portion and an upper surface portion of the columnar convex portions, In addition, a second conductivity type semiconductor layer is formed in each surface region between two adjacent columnar protrusions.

1-1. Substrate The substrate is made of a compound semiconductor substrate such as GaAs or an elemental semiconductor substrate such as Si. The substrate may be single crystal or polycrystalline. The first conductivity type means n-type or p-type. The impurity concentration of the substrate is preferably 1 × 10 ¹⁴ to 1 × 10 ¹⁷ cm ⁻³ . It is particularly preferable to use a p-type silicon single crystal substrate having an impurity concentration of about 1 × 10 ¹⁵ cm ^{−3 as the} substrate.

1-2. Columnar convex part It is preferable that the substrate has a substantially horizontal surface, and a plurality of columnar convex parts are formed on the surface. The columnar convex portion may be thinner toward the upper surface portion (may be a forward taper shape), may be the same thickness, or may be thicker (may be a reverse taper shape). . In the case of the forward tapered shape, the incident angle to the side surface portion of the columnar convex portion is small with respect to the light incident on the solar cell, and thus the reflectance of the light can be reduced. On the other hand, in the case of an inversely tapered shape, with respect to light reflected by each surface region (for example, a region other than a portion on the substrate surface where the columnar convex portion is formed) between two adjacent columnar convex portions. Since the incident angle to the side surface portion of the columnar convex portion becomes small, the reflectance of the light can be reduced.

  The forward taper angle (see θ in FIG. 5) is preferably 90 to 135 ° with respect to the substrate surface. When the angle is larger than 90 °, the incident angle to the side surface portion of the columnar convex portion is smaller than that when the columnar convex portion has the same thickness toward the upper surface portion with respect to the light incident on the solar cell. This is because the reflectance can be reduced. When the angle is smaller than 135 °, the light reflected by the side surface of the columnar convex portion is directed to each surface region between two adjacent columnar convex portions.

  The reverse taper angle (see θ in FIG. 6) is preferably 45 to 90 ° with respect to the substrate surface. If it is larger than 45 °, it is possible to increase the opportunity to further reflect the light reflected by the region other than the side surface of the columnar convex portion or the portion where the columnar convex portion is formed. For the light reflected by each surface region between the two columnar convex portions, the incident angle to the side surface portion of the columnar convex portion is smaller than when the columnar convex portions have the same thickness toward the upper surface portion. This is because the reflectance of the light can be reduced.

  Further, the shape of the upper surface portion of the columnar convex portion is preferably substantially circular, but may be an ellipse or a polygon such as a quadrangle or a hexagon. The diameter of the circle circumscribing the upper surface portion of the columnar convex portion can be, for example, 0.1 to 100 μm, and preferably 10 to 50 μm. If it is larger than 10 μm, the number of carriers in the columnar convex portion of the first conductivity type semiconductor substrate is large, and there is a sufficient number of carriers to obtain solar energy and become a current. This is because high-density columnar convex portions can be formed on the semiconductor substrate, and as a result, the reflectance of sunlight can be reduced.

  The distance between the columnar protrusions (the distance between the closest points between two adjacent columnar protrusions) can be, for example, 0.1 to 100 μm, and preferably 10 to 50 μm. When the angle is larger than 10 μm, when the horizontal angle on the surface of the solar cell substrate is 0 °, even when the incident angle of sunlight is close to 0 °, the sun is formed on the side surface of the columnar convex portion of the first conductivity type semiconductor substrate. This is because the light irradiated and the light reflected by the columnar protrusion can be absorbed by another adjacent columnar protrusion, and when it is smaller than 50 μm, the high density columnar protrusion on the first conductivity type semiconductor substrate. This is because the reflectance of sunlight can be reduced.

  The height of the columnar convex portion can be set to 0.1 to 50 μm, for example, and is preferably set to 20 to 50 μm. If it is larger than 20 μm, there are many opportunities to absorb sunlight since the area of the side surface of the columnar convex portion is large, and the area of the region other than the columnar convex portion is supplemented with the area of the side surface of the columnar convex portion. This is because the power generation amount in the PN junction region hidden by the wiring can be compensated. In addition, when it is smaller than 50 μm, ion implantation for making the side surface of the columnar convex portion an impurity semiconductor layer can be sufficiently performed, and incident solar light can be efficiently irradiated to the side surface of the columnar convex portion.

  The columnar protrusion can be formed, for example, by covering a portion that becomes the upper surface portion of the columnar protrusion with a photoresist or the like and etching a portion that is not covered with the photoresist or the like by an RIE method or the like. Changing the size or height of the circle circumscribing the top surface of the columnar protrusion, or the distance between the columnar protrusions, etc. by changing the size or position of the part covered with photoresist or the like Can do. Further, the diameter of the circle circumscribing the upper surface portion of the columnar projection can be reduced by thermally oxidizing the columnar projection and then removing the oxide film. Further, the taper angle of the columnar convex portion can be changed by changing the content of oxygen contained in the etching gas. Since the columnar convex part of this invention can be formed using normal photolithography and an etching technique, it can hold down manufacturing cost low.

1-3. Second-conductivity-type semiconductor layer Further, second-conductivity-type semiconductor layers are formed in the side surface portion and the upper surface portion of the columnar convex portion and in each surface region between two adjacent columnar convex portions.

  The second conductivity type is n-type or p-type, and is a conductivity type different from the first conductivity type.

The impurity concentration of the side surface portion of the columnar convex portion and the semiconductor layer of the upper surface portion may be the same or different, but when a contact is formed on the upper surface portion, the impurity concentration of the upper surface portion is changed to that of the side surface portion. It is preferable to make it higher than the impurity concentration. This is because by increasing the impurity concentration of the upper surface portion, the contact resistance between the upper surface portion and the contact can be reduced, which contributes to the improvement of photoelectric conversion efficiency. The impurity concentration of the side surface portion is preferably 1 × 10 ¹⁷ to 1 × 10 ²⁰ cm ^−3, and more preferably about 1 × 10 ¹⁸ cm ⁻³ . The impurity concentration of the upper surface portion is preferably 1 × 10 ¹⁸ to 1 × 10 ²² cm ^−3, and more preferably about 1 × 10 ²⁰ cm ⁻³ . The impurity concentration in each surface region between two adjacent columnar convex portions is preferably 1 × 10 ¹⁷ to 1 × 10 ²⁰ cm ^−3, and more preferably about 1 × 10 ¹⁸ cm ⁻³ .

In addition, when an elongated electrode is provided on the surface region, it is preferable that the impurity concentration of the electrode forming portion for forming the elongated electrode is higher than the impurity concentration of the side surface portion of the columnar convex portion. This is because by increasing the impurity concentration at the electrode formation site, the contact resistance between the substrate and the electrode can be reduced, which contributes to an improvement in photoelectric conversion efficiency. The impurity concentration at the electrode formation site is preferably 1 × 10 ¹⁸ to 1 × 10 ²² cm ^−3, and more preferably about 1 × 10 ²⁰ cm ⁻³ .

  Since the pn junction is formed in the side surface portion and the upper surface portion of the columnar convex portion and each surface region between two adjacent columnar convex portions, light can be absorbed at these portions. Incident light to the side surface portion of the columnar convex portion is absorbed by the side surface portion of the columnar convex portion or reflected by the surface of the side surface portion. The reflected light travels to each surface region between two adjacent columnar convex portions. Light directed to each surface region is either absorbed by that region or reflected at the surface of that region. The reflected light travels again to the side surface of the columnar convex portion.

  Thus, in the solar cell of the present invention, incident light can have multiple opportunities to be absorbed by the solar cell. Therefore, in the solar cell of the present invention, incident light can be used effectively, and as a result, high photoelectric conversion efficiency can be obtained.

  Further, in the solar cell of the present invention, even when the incident angle to the solar cell is large, the incident angle to the side surface portion of the columnar convex portion is small, and as a result, the reflectance on the solar cell surface can be reduced. it can.

  The semiconductor layer of the second conductivity type can be formed by performing ion implantation on the side surface portion and the upper surface portion of the columnar convex portion and each surface region between two adjacent columnar convex portions.

  The semiconductor layer of the second conductivity type may be formed by a CVD method or the like through an insulating film formed by the CVD method or the like. In this case, a PIN junction solar cell is obtained.

2. Second Embodiment A solar cell according to a second embodiment of the present invention is the solar cell according to the first embodiment, wherein the insulating layer is formed on the substrate so as to cover and planarize the columnar protrusions. And elongate wirings formed on the insulating layer and contacts provided on the columnar protrusions, and the columnar protrusions and the elongate wirings are electrically connected by the contacts provided on the columnar protrusions. Connected.

  By protecting the columnar protrusions with the insulating layer, the columnar protrusions can be prevented from being damaged. The insulating layer is made of a silicon oxide film formed by HDP-CVD or the like.

  A contact hole can be formed on each columnar convex portion by forming a contact hole in the insulating layer from above each columnar convex portion and filling the contact hole with tungsten or the like. In addition, an elongated wiring for electrically connecting the contact of each columnar convex portion is formed on the insulating layer with aluminum or the like.

  Since each columnar convex part and the elongated wiring are electrically connected by a contact provided on each columnar convex part, the distance between each columnar convex part and the wiring can be shortened and generated at the columnar convex part. Can be efficiently sent to the wiring.

  The width of the elongated wiring can be made smaller than the diameter of a circle circumscribing the upper surface portion of the columnar convex portion. In this case, if the number of columnar convex portions is the same, the area occupied by the upper surface portion of the columnar convex portions on the substrate is relatively large, so that a large amount of light can be absorbed by the upper surface portion of the columnar convex portions. . Further, the width of the elongated wiring may be larger than the diameter of a circle circumscribing the upper surface portion of the columnar convex portion. In this case, if the number of columnar convex portions is the same, the area occupied by each surface region between two adjacent columnar convex portions on the substrate is relatively large, so that a large amount of light is absorbed in that region. Can do.

3. Third Embodiment A solar cell according to a third embodiment of the present invention is the solar cell according to the first embodiment, and includes an elongated electrode on a surface region between two adjacent columnar protrusions.

  In the second embodiment, since the contact is provided on the upper surface of the columnar convex portion, a part of the incident light is reflected on the upper surface of the columnar convex portion. On the other hand, in the present embodiment, the light incident on the top surface of the columnar convex portion is photoelectrically converted on the front surface, and the light incident on the bottom surface of the columnar convex portion is also reflected multiple times on the side surface of the adjacent columnar convex portion. Use efficiency improves.

  The elongated electrode is preferably arranged so as to be adjacent to at least one, preferably a plurality of columnar protrusions. In this case, the carriers generated in the columnar protrusions are efficiently carried to the electrode, so that loss due to recombination can be reduced. Note that “adjacent to the columnar protrusions” includes a case of contacting the columnar protrusions.

  The elongated electrode is made of, for example, polycrystalline silicon. The elongated electrode can be formed, for example, by forming a material layer on the substrate, forming an elongated mask layer on the surface region, and isotropically etching the material layer in that state. The material layer is made of a conductor or a semiconductor doped with impurities. An example of the semiconductor is polycrystalline silicon. The semiconductor is preferably doped with a second conductivity type impurity. The mask layer is made of a photoresist or the like. Further, for example, when the material layer is made of polycrystalline silicon, isotropic etching is performed by, for example, a method called chemical dry etching (CDE) in which various films on the surface of a semiconductor substrate are shaved by a method that causes a chemical reaction in a gas phase. Can be implemented. By isotropically etching the material layer, the material layer such as the upper surface and the side surface of the columnar protrusion is effectively removed, and an elongated electrode can be formed on the surface region.

  When the elongated electrode is formed in contact with the columnar convex portion, etching of the side surface of the columnar convex portion may be hindered by the mask layer covering the portion where the elongated electrode is formed. In that case, the material layer on the side surface of the columnar convex portion may be removed in advance before forming the mask layer. The material layer on the side surface of the columnar convex portion can be removed, for example, by forming another mask layer that exposes only the side surface of the columnar convex portion and performing isotropic etching using the mask layer. . This mask layer can be formed, for example, by forming a silicon oxide film covering the entire surface of the substrate by HDP-CVD and etching back the silicon oxide film. The mask layer that exposes only the side surfaces of the columnar convex portions can be formed by this method because the silicon oxide film formed by the HDP-CVD method is formed thinner than the other portions on the side surfaces of the columnar convex portions. This is because that.

By the way, the second conductivity type semiconductor layer can be formed by forming a polycrystalline silicon layer containing the second conductivity type impurity on the substrate and diffusing the impurities in the polycrystalline silicon layer. The diffusion of impurities in the polycrystalline silicon layer is performed, for example, by heat-treating the substrate on which the polycrystalline silicon layer is formed at 1200 ° C. for about 600 minutes. When forming the second conductivity type semiconductor layer by ion implantation or the like, it may be difficult to form the second conductivity type semiconductor layer if the height of the columnar convex portion is increased. The height limitation of the columnar protrusion is relaxed. The impurity concentration in the polycrystalline silicon layer is preferably about 1 × 10 ¹⁵ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ . Such a polycrystalline silicon layer can be formed by, for example, a method of creating an impurity atmosphere to be introduced into the reaction chamber and laminating the polycrystalline silicon layer while introducing impurities.

  Moreover, the solar cell of this embodiment may further include an insulating layer formed on the substrate so as to cover and flatten the elongated electrodes and the columnar protrusions. By providing the insulating layer, it is possible to prevent the elongated electrodes and the columnar protrusions from being damaged.

  FIG. 1 is a plan view showing the structure of the solar cell 1 according to the first embodiment. 2A is a cross-sectional view taken along the line II in FIG. 1, and FIG. 2B is a cross-sectional view taken along the line II-II in FIG.

  The solar cell 1 includes a p-type silicon substrate 5 having a plurality of columnar protrusions 3 on the surface. The side surface portion 3a and the upper surface portion 3b of the columnar convex portion 3 and each surface region between the two adjacent columnar convex portions (regions other than the portion on the substrate surface where the columnar convex portion is formed) 5a A type semiconductor layer is formed.

  In addition, as shown in FIG. 2, an insulating layer 9 formed on the substrate 5 so as to cover the columnar protrusions 3 and an elongated wiring 11 formed on the insulating layer 9 are further provided. Each columnar protrusion 3 and the elongated wiring 11 are electrically connected by a contact 13 provided on each columnar protrusion 3.

  Hereafter, the manufacturing process of such a solar cell is demonstrated.

  First, by covering the portion to be the upper surface portion 3b of the columnar convex portion 3 with a photoresist and etching the portion not covered with the photoresist by, for example, an RIE method under a condition in which oxygen gas is added to normal Si etching conditions, A plurality of columnar protrusions 3 are formed on the silicon substrate 5.

  Next, for example, phosphorus is ion-implanted, for example, at a tilt angle of 7 ° and a rotation angle of 45 + 90 × n into the side surface portion 3a and the upper surface portion 3b of the columnar convex portion 3 and each surface region 5a between two adjacent columnar convex portions. By performing under the condition (n = 0, 1, 2, 3), an n-type semiconductor layer is formed.

Next, an insulating layer 9 made of SiO ₂ is formed on the substrate 5 so as to cover the columnar protrusions 3 by HDP-CVD, a contact hole is formed in the insulating layer 9, and the contact hole is filled with tungsten or the like. A contact 13 is formed on each columnar protrusion 3.

  Next, the wiring 11 that electrically connects the contacts 13 of the columnar protrusions 3 is formed to obtain the structure shown in FIGS.

FIG. 3 is a cross-sectional view illustrating the structure of the solar cell 21 according to the second embodiment. The difference from the first embodiment is that the width of the elongated wiring 11 is larger than the diameter of a circle circumscribing the upper surface portion 3 b of the columnar convex portion 3.
In this case, if the number of the columnar convex portions is the same, the area occupied by each surface region 5a between the two adjacent columnar convex portions 3 on the substrate 5 is relatively large. Can be absorbed.

FIG. 4 is a cross-sectional view illustrating the structure of the solar cell 31 according to the third embodiment. The difference from the first embodiment is that the width of the elongated wiring 11 is smaller than the diameter of a circle circumscribing the upper surface portion 3 b of the columnar convex portion 3.
In this case, if the number of the columnar convex portions is the same, the area occupied by the upper surface portion 3b of the columnar convex portion on the substrate 5 is relatively large, so that a large amount of light is absorbed by the upper surface portion 3b of the columnar convex portion. be able to.

  FIG. 5 is a cross-sectional view illustrating the structure of the solar cell 41 according to the fourth embodiment. The difference from the first embodiment is that the columnar convex portion 3 is thinner toward the upper surface portion 3b of the columnar convex portion 3, that is, has a forward tapered shape. θ represents the taper angle with respect to the surface of the substrate 5. In this case, since the incident angle to the side surface part 3a of the columnar convex part 3 becomes small with respect to the light incident on the solar cell 41, the reflectance of the light can be reduced. The taper angle can be changed by changing the content of oxygen contained in the etching gas.

  FIG. 6 is a cross-sectional view illustrating the structure of the solar cell 51 according to the fifth embodiment. The difference from the first embodiment is that the columnar convex portion 3 is thicker toward the upper surface portion 3b of the columnar convex portion 3, that is, has an inversely tapered shape. θ represents the taper angle with respect to the surface of the substrate 5. In this case, since the incident angle to the side surface portion 3a of the columnar convex portion 3 becomes small with respect to the light reflected by each surface region 5a between two adjacent columnar convex portions, the reflectance of the light should be reduced. Can do. The taper angle can be changed by changing the content of oxygen contained in the etching gas.

  FIG. 7 is a cross-sectional view illustrating the structure of the solar cell 61 according to the sixth embodiment. The difference from the first embodiment is that the impurity concentrations of the upper surface portion 3b of the columnar convex portion 3 and the semiconductor layer of the side surface portion 3a are equal.

  FIG. 8 is a plan view showing the structure of the solar cell 71 according to the seventh embodiment. The difference from Example 1 is that the shape of the upper surface part 3b of the columnar convex part 3 is a square. Even if it is such a shape, the effect of the present invention can be obtained.

  FIG. 9 is a plan view illustrating the structure of the solar cell 81 according to the eighth embodiment. The difference from the first embodiment is that the shape of the upper surface portion 3b of the columnar convex portion 3 is a polygon. Even if it is such a shape, the effect of the present invention can be obtained.

  FIG. 10 is a plan view illustrating the structure of the solar cell 91 according to the ninth embodiment. 11A is a cross-sectional view taken along the line II in FIG. 10, and FIG. 11B is a cross-sectional view taken along the line II-II in FIG.

  The solar cell 91 includes a p-type silicon substrate 5 having a plurality of columnar protrusions 3 on the surface. The side surface portion 3a and the upper surface portion 3b of the columnar convex portion 3 and each surface region between the two adjacent columnar convex portions (regions other than the portion on the substrate surface where the columnar convex portion is formed) 5a A type semiconductor layer is formed. An elongated electrode 15 made of n-type polycrystalline silicon is formed on the surface region 5a. The elongated electrode 15 is disposed so as to be adjacent to the plurality of columnar protrusions 3.

Hereafter, the manufacturing process of such a solar cell is demonstrated.
First, a silicon substrate 5 having a plurality of columnar protrusions 3 is formed in the same process as in the first embodiment.
Next, a polycrystalline silicon layer (n ⁺ -doped) is formed on the entire surface of the substrate 5 so as to cover the columnar protrusions 3, and heat treatment is performed at 1200 ° C. for 600 minutes, so that impurities in the polycrystalline silicon layer are removed from the substrate 5. And it diffuses in the columnar convex part 3, and forms an n-type semiconductor layer. Here, the polycrystalline silicon layer is formed by, for example, a method of creating an impurity atmosphere to be introduced into the reaction chamber and laminating the polycrystalline silicon layer while introducing impurities. The impurity concentration of the polycrystalline silicon layer is about 1 × 10 ¹⁵ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ .
Next, an elongated mask layer is formed with a photoresist on the surface region between two adjacent columnar convex portions, and the polycrystalline silicon layer is isotropically etched in this state, thereby forming the elongated electrode 15.

It is a top view which shows the structure of the solar cell which concerns on Example 1 of this invention. (A) is II sectional drawing in FIG. 1, (b) is II-II sectional drawing in FIG. It is sectional drawing which shows the structure of the solar cell which concerns on Example 2 of this invention. It is sectional drawing which shows the structure of the solar cell which concerns on Example 3 of this invention. It is sectional drawing which shows the structure of the solar cell which concerns on Example 4 of this invention. It is sectional drawing which shows the structure of the solar cell which concerns on Example 5 of this invention. It is sectional drawing which shows the structure of the solar cell which concerns on Example 6 of this invention. It is a top view which shows the structure of the solar cell which concerns on Example 7 of this invention. It is a top view which shows the structure of the solar cell which concerns on Example 8 of this invention. It is a top view which shows the structure of the solar cell which concerns on Example 9 of this invention. (A) is II sectional drawing in FIG. 10, (b) is II-II sectional drawing in FIG.

Explanation of symbols

1, 21, 31, 41, 51, 61, 71, 81 Solar cell 3 Plural columnar convex portions 3 a Side surface portion 3 b of the columnar convex portion Upper surface portion 5 of the columnar convex portion Silicon substrate 5 a Between two adjacent columnar convex portions Each surface region 9 Insulating layer 11 Elongated wiring 13 Contact 15 Elongated electrode

Claims (12)

  A first conductivity type semiconductor substrate having a plurality of columnar protrusions on the surface; a side surface and an upper surface of the columnar protrusion; and a second conductivity type in each surface region between two adjacent columnar protrusions. A solar cell in which a semiconductor layer is formed.   The solar cell according to claim 1, wherein the columnar convex portion becomes thinner toward an upper surface portion of the columnar convex portion.   The solar cell according to claim 1, wherein the columnar convex portion becomes thicker toward an upper surface portion of the columnar convex portion.   2. The solar cell according to claim 1, wherein the semiconductor layer on the upper surface portion of the columnar convex portion has an impurity concentration higher than that of the semiconductor layer on the side surface portion of the columnar convex portion.   Further comprising: an insulating layer formed on the substrate so as to cover and flatten the columnar protrusions; an elongated wiring formed on the insulating layer; and a contact provided on each columnar protrusion. The solar cell according to claim 1, wherein the convex portion and the elongated wiring are electrically connected by a contact provided on each columnar convex portion.   The solar cell according to claim 5, wherein the elongated wiring has a width smaller than a diameter of a circle circumscribing the upper surface portion of the columnar convex portion.   The solar cell according to claim 5, wherein the elongated wiring has a width larger than a diameter of a circle circumscribing the upper surface portion of the columnar convex portion.   The solar cell of Claims 1-4 provided with an elongate electrode on the surface area | region between two adjacent columnar convex parts.   The solar cell according to claim 8, wherein the elongated electrode is disposed adjacent to the plurality of columnar protrusions.   The solar cell according to claim 8, wherein the elongated electrode is made of polycrystalline silicon.   5. The method of manufacturing a solar cell according to claim 1, wherein a second layer is formed by forming a polycrystalline silicon layer containing a second conductivity type impurity on a substrate and diffusing the impurities in the polycrystalline silicon layer. A method for manufacturing a solar cell comprising a step of forming a conductive semiconductor layer.   11. The method for manufacturing a solar cell according to claim 10, wherein a polycrystalline silicon layer containing a second conductivity type impurity is formed on a substrate, an elongated mask layer is formed on the surface region, A method for manufacturing a solar cell comprising a step of forming an elongated electrode made of polycrystalline silicon by isotropic etching of a crystalline silicon layer.

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