KR101760011B1 - Solar cell and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a method of manufacturing a solar cell, comprising: forming an emitter portion of a second conductivity type opposite to the first conductivity type on a first surface of a substrate of a first conductivity type by ion implantation; Forming a protective layer on the second surface of the substrate opposite to the first surface of the substrate; forming a first electrode connected to the emitter and a second electrode selectively connected to the substrate through the protective layer; . Since the emitter portion is formed only on the first surface of the desired substrate, the step of removing the emitter portion formed on the undesired surface is unnecessary. As a result, the manufacturing cost and manufacturing time of the solar cell are reduced.

Description

SOLAR CELL AND METHOD FOR MANUFACTURING THE SAME

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

Recently, as energy resources such as oil and coal are expected to be depleted, interest in alternative energy to replace them is increasing, and solar cells that produce electric energy from solar energy are attracting attention.

Typical solar cells have a semiconductor portion that forms a p-n junction by different conductive types, such as p-type and n-type, and electrodes connected to semiconductor portions of different conductivity types, respectively.

When light is incident on such a solar cell, a plurality of electron-hole pairs are generated in the semiconductor, and the generated electron-hole pairs move in the corresponding directions, that is, electrons, toward the n- Move to the negative side. The transferred electrons and holes are collected by the different electrodes connected to the p-type semiconductor portion and the n-type semiconductor portion, respectively, and the electrodes are connected by a wire to obtain electric power.

SUMMARY OF THE INVENTION The present invention has been made in an effort to reduce the manufacturing time of a solar cell.

Another technical problem to be solved by the present invention is to reduce manufacturing cost of a solar cell.

According to an aspect of the present invention, there is provided a method of manufacturing a solar cell, comprising: forming an emitter portion of a second conductivity type opposite to the first conductivity type on a first surface of a substrate having a first conductivity type, Forming a protective film on a second surface of the substrate opposite to the first surface of the substrate; forming a first electrode connected to the emitter and a second electrode selectively connected to the substrate through the protective film; .

The method may further include forming first and second thermal oxide films on the first and second surfaces of the substrate when the emitter is formed, Wherein the protective film is formed on the second thermal oxide film located on the second surface of the substrate and the first electrode is connected to the emitter portion via the first thermal oxide film located on the first surface of the substrate And the second electrode may be connected to the substrate through the protective film and the second thermal oxide film.

The first and second thermal oxide film forming steps may be performed at a temperature of 700 ° C to 900 ° C.

The method may further include forming an anti-reflection portion on the first thermal oxide film located on the first surface of the substrate, wherein the first electrode includes the anti-reflection portion, And may be connected to the substrate through a first thermal oxide film.

The anti-reflection part may be formed of silicon nitride to form the anti-reflection part.

The first and second thermal oxide films may each have a thickness of 15 nm to 30 nm.

The protective film forming step may form the protective film with silicon nitride.

The method of manufacturing a solar cell according to the above feature may further include forming an anti-reflection portion on the emitter portion, and the first electrode may be connected to the emitter portion through an anti-reflection portion.

The anti-reflection portion may be formed of a silicon nitride film.

The protective layer forming step may include forming a first protective layer with silicon oxide, and forming a second protective layer with silicon nitride.

The protective film forming step may include forming a first protective film with aluminum oxide, and forming a second protective film with silicon nitride.

The first conductivity type may be p-type, and the second conductivity type may be n-type.

The method may further include forming a texturing surface on the first and second surfaces of the substrate prior to forming the emitter portion, And may be formed on the first and second surfaces, respectively.

The emitter forming step may include implanting an impurity of the second conductivity type into the first surface of the substrate by the ion implantation method to form an impurity layer on the first surface, And heat treating the substrate to convert the impurity layer into the emitter portion.

A solar cell according to another aspect of the present invention includes a substrate having a first conductive type and having first and second surfaces located opposite to each other and having a textured surface having a plurality of projections and depressions, A first electrode located only on a first surface of the substrate and having a second conductivity type opposite to the first conductivity type, a first electrode electrically connected to the emitter portion, a protective layer disposed on the second surface of the substrate, A first electrode connected to the emitter portion, and a second electrode selectively connected to the substrate through the protection film.

The emitter portion has a resistance of 60? / Sq. Lt; / RTI > to 120 ohms / sq.

The solar cell may further include a first thermal oxide film located on the emitter and a second thermal oxide film located on the second surface of the substrate, wherein the protective film is located on the second thermal oxide film The first electrode may be connected to the emitter via the first thermal oxide film, and the second electrode may be connected to the substrate through the protective film and the second thermal oxide film.

The first and second thermal oxide films may each have a thickness of 15 nm to 30 nm.

The protective film may be made of silicon nitride.

The protective film may have a thickness of 40 nm to 80 nm.

The solar cell according to the above feature may further include an antireflection unit positioned on the first thermal oxide film.

The anti-reflection portion may be made of silicon nitride.

The solar cell according to the above feature may further include an antireflective portion positioned on the emitter portion, and the first electrode may contact the emitter portion through the antireflective portion.

The anti-reflection portion may be made of silicon nitride.

The protective layer may include a first protective layer made of silicon oxide and a second protective layer disposed on the second surface of the substrate, the second protective layer being formed on the first protective layer and made of silicon nitride.

The first protective film may have a thickness of 200 nm to 300 nm, and the second protective film may have a thickness of 40 nm to 80 nm.

The first conductivity type may be p-type and the second conductivity type may be n-type.

The protective layer may include a first protective layer made of aluminum oxide and a second protective layer disposed on the second surface of the substrate, the second protective layer being formed on the first protective layer and made of silicon nitride.

The first protective film may have a thickness of 30 nm to 70 nm, and the second protective film may have a thickness of 40 nm to 80 nm.

The first conductivity type may be p-type and the second conductivity type may be n-type.

The solar cell according to the above feature may further include an electric field portion disposed on the substrate in contact with the second electrode.

The roughness of the first surface and the second surface may be the same.

Each of the plurality of irregularities may have a maximum diameter and a height of 5 mu m to 15 mu m.

Each of the plurality of irregularities may have an aspect ratio of 0.5 to 2.

According to this feature, since the emitter portion is formed only on the surface of the desired substrate, the step of removing the emitter portion formed on the undesired surface is unnecessary. As a result, the manufacturing cost and manufacturing time of the solar cell are reduced.

1 is a partial perspective view of a battery according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of the solar cell shown in FIG. 1 taken along line II-II.
3A to 3J are views sequentially showing an example of a method of manufacturing a solar cell according to an embodiment of the present invention.
4 is a partial perspective view of a solar cell according to another embodiment of the present invention.
5 is a cross-sectional view of the solar cell shown in FIG. 4 cut along the line VV.
6A to 6G are views sequentially showing an example of a method of manufacturing a solar cell according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out 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 order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. 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. Conversely, when a part is "directly over" another part, it means that 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.

Hereinafter, a solar cell according to an embodiment of the present invention will be described with reference to the accompanying drawings.

First, an example of a solar cell according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. FIG.

1, an example of a solar cell 11 according to an embodiment of the present invention includes a substrate 110, an incident surface (hereinafter referred to as a front surface) that is a surface of a substrate 110 on which light is incident, An antireflective portion 130 positioned on the emitter portion 121 and a surface of the substrate 110 opposite to the front surface of the substrate 110 A front electrode part 140 connected to the emitter part 121, a rear electrode part 150 positioned on the protective part 190 and connected to the substrate 110, And a plurality of back surface field portions 172 selectively located on the back surface of the substrate 110.

The substrate 110 is a semiconductor substrate made of a semiconductor of the first conductivity type, for example, silicon of p-type conductivity type. At this time, the semiconductor is a crystalline semiconductor such as monocrystalline silicon or polycrystalline silicon.

Impurities of a trivalent element such as boron (B), gallium (Ga), indium (In) and the like are doped in the substrate 110 when the substrate 110 has a p-type conductivity type. Alternatively, however, the substrate 110 may be of the n-type conductivity type and may be made of a semiconductor material other than silicon. When the substrate 110 has an n-type conductivity type, impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb) are doped in the substrate 110.

1 and 2, a separate texturing treatment process is performed on the front and rear surfaces of the substrate 110, and the front and rear surfaces of the substrate 110 have a textured surface, which is an uneven surface having a plurality of irregularities . In this case, the emitter 121 and the reflection preventing part 130, and the protecting part 190 and the rear electrode part 150 located on the front and rear surfaces of the substrate 110 also have uneven surfaces.

Since the entire surface of the substrate 110 is textured, the incident area of the substrate 110 increases and the light reflectivity decreases due to a plurality of reflection operations due to the irregularities, so that the amount of light incident on the substrate 110 increases The efficiency of the solar cell 11 is improved. In addition, since the rear surface of the substrate 110 is textured, light passing through the substrate 110 is reflected back toward the substrate 110 by the rear surface of the textured substrate 110, The amount of light re-incident into the substrate 110 increases. For convenience, the concavities and convexities of the texturing surface in FIGS. 1 and 2 all have the same maximum diameter (a) and height (b), but actually the size of the maximum diameter (a) Are randomly determined, so that a plurality of irregularities having different maximum diameters (a) and (b) are formed.

In this example, the maximum diameter (a) and the width (b) of each unevenness formed on the front surface and the rear surface of the substrate 110 may be 5 占 퐉 to 15 占 퐉, and the vertical and horizontal portions b / 2 < / RTI >

At this time, since the texturing surfaces formed on the front and rear surfaces of the substrate 110 are formed by one process, the roughness of the textured surface per unit area is the same on the front surface and the rear surface of the substrate 110.

The emitter portion 121 located on the substrate 110 is an impurity portion having a second conductivity type opposite to the conductivity type of the substrate 110, for example, an n-type conductivity type. Thus forming a p-n junction with the first conductive type portion of the substrate 110.

Due to the built-in potential difference due to the pn junction, the electron-hole pairs generated by the light incident on the substrate 110 are separated into electrons and holes, electrons move toward the n-type, Moves toward the p-type. Accordingly, when the substrate 110 is p-type and the emitter section 121 is n-type, the separated holes move toward the substrate 110, and the separated electrons move toward the emitter section 121.

Since the emitter section 121 forms a pn junction with the substrate 110, the emitter section 121 has a p-type conductivity type when the substrate 110 has an n-type conductivity type, unlike the present embodiment . In this case, the separated electrons move toward the substrate 110, and the separated holes move toward the emitter 121.

When the emitter section 121 has an n-type conductivity type, the emitter section 121 is formed by implanting an impurity of a pentavalent element into the substrate 110 by ion implantation. Conversely, the emitter section 121 is formed of a p- The impurity of the trivalent element is implanted into the substrate 110 by an ion implantation method. The emitter layer 121 is formed only on one surface of the substrate 110, for example, on the front surface of the substrate 110. The ion implantation method may be applied to the ion implantation process, Accordingly, the doping amount (ion implantation amount) and the doping depth (ion implantation depth) of the impurity implanted into the substrate 110 are changed, and the ion generation amount and the ion speed are easily controlled by using the power applied during the ion implantation process. Therefore, it is easier to control the amount of impurities implanted into the substrate 110 and the doping depth of the impurity when the emitter layer 121 is formed by ion implantation than when the impurities are doped into the substrate 110 using the thermal diffusion method.

  For example, the ion implantation energy may be, for example, about 100 KeV to 3 MeV, and the resulting doping depth may be about 0.5 [mu] m to 10 [mu] m from the surface of the substrate 110 as an example.

In addition, since it is easy to control the implantation amount and the implantation depth of the ions, the emitter section 121 has a higher value of about 60? / Sq. To about 120 < RTI ID = 0.0 > OMEGA / sq. ≪ / RTI > As a result, the impurity doping concentration of the emitter section 121 of the present example is reduced and the impurity doping thickness of the emitter section 121 is reduced as compared with the emitter section by the heat diffusion method, so that the loss amount of the electric charges lost by the impurities is greatly reduced .

When the emitter section 121 has a sheet resistance value of about 60? / Sq. Or more, the amount of light absorbed by itself through the emitter section 121 is reduced, the amount of reduction of light incident into the substrate 110 is further reduced, The amount of charge lost by the impurities existing in the emitter portion 121 is further reduced.

When the emitter layer 121 has a sheet resistance value of about 120? / Sq. Or less, a more stable pn junction is formed with the substrate 110, so that electrons and charges are generated more stably and the front electrode part 140 and the emitter part 121 to prevent defects in the shunt contacting the substrate 110.

The antireflective portion 130 located on the emitter portion 121 having the textured surface reduces the reflectivity of the light incident on the solar cell 11 and increases the selectivity of the specific wavelength region to increase the efficiency of the solar cell 11.

The antireflective portion 130 may be made of transparent and hydrogenated silicon nitride (SiNx), has a thickness of about 70 nm to about 80 nm, and may have a refractive index of about 2.0 to 2.1.

When the refractive index of the antireflection unit 130 is 2.0 or more, the amount of light absorbed by the antireflection unit 130 itself is further reduced while the reflectivity of light is reduced. When the refractive index of the antireflection unit 130 is 2.1 or less, The reflectivity of the antireflection portion 130 is further reduced.

In this example, the refractive index (2.0 to 2.1) of the antireflection portion 130 has a value between the refractive index (about 1) of air and the refractive index (about 3.5) of the substrate 110. Accordingly, since the change in the refractive index from the air toward the substrate 110 sequentially increases, the reflectivity of light is further reduced by the change in the refractive index, and the amount of light incident on the substrate 110 is further increased.

Further, when the thickness of the antireflecting portion 130 is about 70 nm or more, a more effective effect of preventing reflection of light is obtained. When the thickness of the antireflective portion 130 is about 80 nm or less, the amount of light absorbed by the antireflective portion 130 itself is reduced to increase the amount of light incident on the substrate 110, The front electrode part 140 passes through the reflection preventing part 130 more easily and smoothly so that the front electrode part 140 and the emitter part 121 are more stably and smoothly connected.

The antireflection portion 130 contains hydrogen (H) by the hydrogen (H) applied when the antireflection portion 130 is formed. Therefore, the antireflective portion 130 is also changed into a stable bond due to the contained hydrogen (H), such as a dangling bond existing on the surface of the substrate 110 and its vicinity And a passivation function is executed to reduce the disappearance of the charges that have moved toward the surface of the substrate 110 due to the defect. Therefore, the amount of charge lost due to defects is reduced by the antireflection portion 130.

1 and 2, the antireflection portion 130 has a single-layer structure, but may have a multilayer structure such as a double-layer structure and may be omitted as necessary.

The front electrode unit 140 includes a plurality of front electrodes 141 and a plurality of front bus bars 142 connected to the plurality of front electrodes 141.

The plurality of front electrodes 141 are connected to the emitter section 121, and are spaced apart from each other and extend in a predetermined direction. The plurality of front electrodes 141 collects charges, for example, electrons, which have migrated toward the emitter section 121.

A plurality of front bus bars 142 are connected to the emitter section 121 and extend in a direction crossing the plurality of front electrodes 141.

The plurality of front bus bars 142 are located on the same layer as the plurality of front electrodes 141 and are electrically and physically connected to the front electrodes 141 at the intersections of the front electrodes 141.

1, the plurality of front electrodes 141 has a stripe shape extending in the horizontal or vertical direction, and the plurality of front bus bars 142 have stripe shapes extending in the vertical or horizontal direction And the front electrode unit 140 is disposed on the front surface of the substrate 110 in a lattice form.

Each front bus bar 142 must collect the charges collected by the plurality of intersecting front electrodes 141 as well as the charge (e.g., electrons) moving from the emitter section 121 and move them in a desired direction, The width of the bar 142 is larger than the width of each front electrode 141.

A plurality of front bus bars 142 are connected to an external device, and output the collected electric charges to an external device.

The front electrode part 140 having the plurality of front electrodes 141 and the plurality of front bus bars 142 is made of at least one conductive material such as silver (Ag). However, in an alternative example, the conductive material may be selected from the group consisting of Ni, Cu, Al, Sn, Zn, In, Ti, Au, Or a combination thereof, but may be made of a conductive material other than the conductive material.

In FIG. 1, the number of the front electrode 141 and the front bus bar 142 located on the substrate 110 is only an example, and may be changed depending on the case.

The protective portion 190 located on the rear surface of the substrate 110 as the textured surface includes the first protective layer 191 located on the rear surface of the substrate 110 and the second protective layer 192 located on the first protective layer 191.

The first protective film 191 may be made of silicon oxide (SiOx) or aluminum oxide (AlxOy). When the first protective film 191 is made of silicon oxide (SiOx), the first protective film 191 may have a thickness of about 200 nm to about 300 nm, and the first protective film 191 may be made of aluminum oxide (AlxOy) When made, may have a thickness of from about 30 nm to about 70 nm.

The second protective film 192 may be made of silicon nitride (SiNx) and may have a thickness of about 40 nm to about 80 nm.

Hydrogen is injected into the process chamber and hydrogen is injected into the first and second protective films 191 and 192 by the injected hydrogen H when the first protective film 191 and the second protective film 192 are formed. . Therefore, defects such as dangling bonds present on the back surface and near the substrate 110 due to the hydrogen (H) contained in the first and second protective films 191 and 192 are converted into stable bonds. As a result, a passivation function for reducing the disappearance of charges due to defects moving toward the surface of the substrate 110 is performed by the first and second protective films 191 and 192, The amount of charge lost at or near the surface is reduced.

The first and second protective films 191 and 192 reflect light passing through the substrate 110 toward the substrate 110 to increase the amount of light incident on the substrate 110.

In addition, the second protective film 192 prevents the hydrogen (H) contained in the first protective film 191 and performing the passivation function from moving to the opposite side of the surface of the substrate 110, The passivation effect is prevented from being reduced by the passivation layer 150 and the passivation effect of the surface of the substrate 110 is further improved.

In general, silicon nitride (SiNx) has a positive positive charge characteristic and aluminum oxide (AlxOy) has a negative negative charge characteristic.

Therefore, when the substrate 110 has a p-type conductivity type, when the passivation function is performed by placing a film made of silicon nitride (SiNx) directly on the rear surface of the substrate 110, the silicon nitride film is positively charged And the positive holes which are positive charges moving toward the silicon nitride film have the same polarity as that of the silicon nitride film. Therefore, the holes are pushed to the opposite side of the silicon nitride film due to the polarity of the silicon nitride film.

Therefore, when the substrate 110 is of the p-type, the first protective film 190 made of silicon oxide (SiOx) acts not only as passivation but also affects the polarity (+) of the second protective film 192, As shown in Fig. The positive polarity of the silicon oxide (SiOx) prevents the positive polarity from reaching the rear surface of the substrate 110. Hence, the holes generated in the substrate 110 are transferred to the fixed electric charge of the second protective film 192 So that the substrate 110 can be safely and smoothly moved to the rear surface of the substrate 110 without being affected.

Therefore, when the thickness of the first protective film 191 of silicon oxide (SiOx) is about 200 nm or more, the influence of the fixed charge of the second protective film 192 of silicon nitride (SiNx) And the time and cost for manufacturing the first protective film 191 are unnecessarily increased when the thickness of the first protective film 191 made of silicon oxide (SiOx) is about 300 nm or less So that the hole can be stably transported to the rear surface of the substrate 110 without performing any process.

Therefore, in the case where the first protective film 191 is made of silicon oxide (SiOx) and the second protective film 192 is made of silicon nitride (SiNx) in the p-type substrate 110, the passivation function is mainly performed on the first protective film 191 and the first protective film 191 mainly performs a function of preventing the adverse effect on the hole movement due to the fixed charge of the second protective film 192 from being adversely affected.

However, when a film made of aluminum oxide (AlxOy) having a negative (-) fixed charge is placed directly on the p-type substrate 110, holes serving as positive charges moving toward the aluminum oxide film have a polarity opposite to that of the aluminum oxide film The electrons which are negative charges having the same polarity as the aluminum oxide film are pushed to the opposite side of the aluminum oxide film due to the polarity of the aluminum oxide film. Therefore, when aluminum oxide (AlxOy) is used as the first protective film 191 on the p-type substrate 110, the amount of movement of the holes moving toward the back surface of the substrate 110 is further increased due to negative fixed charges .

Therefore, when the first protective film 191 is made of aluminum oxide (AlxOy) and the second protective film 192 is made of silicon nitride (SiNx), the passivation function is mainly performed by the first protective film 191, The passivation layer 192 mainly protects the passivation effect from the rear electrode section 150.

The first protective film 191 made of aluminum oxide does not adversely affect the hole transfer because the fixed charge of the second protective film 192 does not adversely affect the hole transfer. Therefore, when the first protective film 191 is made of aluminum oxide (AlxOy) Lt; RTI ID = 0.0 > thickness. ≪ / RTI > For example, as already described, the first protective film 191 of aluminum oxide (AlxOy) may have a thickness of about 30 nm to about 70 nm.

A more stable and efficient passivation function is performed when the thickness of the first protective film 191 made of aluminum oxide (AlxOy) is about 30 nm or more and the thickness of the first protective film 191 made of aluminum oxide (AlxOy) It is possible to stably move the hole to the rear surface of the substrate 110 without unnecessarily increasing the time and cost for manufacturing the first protective film 191. [

As described above, the amount of charge loss due to defects located on and near the surface of the substrate 110 by the protective portion 190 located on the rear surface of the substrate 110 and composed of the first and second protective films 191 and 192 The efficiency of the solar cell 11 is improved.

A plurality of rear electric fields 172 located on the rear surface of the substrate 110 are p.sup. + Regions in which impurities of the same conductivity type as that of the substrate 110 are doped at a higher concentration than the substrate 110, for example.

A potential barrier is formed due to a difference in impurity concentration between the first conductive region (for example, p-type) of the substrate 110 and each of the rear electric fields 172. As a result, the rear electric field 172, While the hole movement toward the rear electric field 172 becomes easier. Accordingly, the rear electric field 172 reduces the amount of electric charge lost due to the recombination of electrons and holes at the back surface of the substrate 110 and the vicinity thereof, and accelerates the movement of a desired electric charge (e.g., a hole) ) In the direction of the arrow.

The rear electrode unit 150 includes a plurality of rear bus bars 152 positioned on the protection unit 190 and connected to the rear electrode 155 and the rear electrode 155.

The rear electrode 155 is positioned above the portion of the protection 190 except for the portion of the protection 190 where the plurality of rear bus bars 152 are located. However, in an alternative example, the back electrode 155 may not be located at the edge portion of the back surface of the substrate 110.

The rear electrode 155 has a plurality of contacts 151 connected to a plurality of rear electric fields 172 located on the substrate 110 through the protection unit 190. The rear electrode 155 is selectively connected to a portion of the substrate 110, that is, a plurality of rear electric fields 172, via the plurality of contact portions 151. [

As shown in Fig. 1, the plurality of contacts 151 are connected to the substrate 110 in various shapes such as circular, elliptical, or polygonal at regular intervals, for example, intervals of about 0.5 mm to about 1 mm. However, in an alternative example, each contact portion 151 may have a stripe shape elongated in one direction while being electrically connected to the substrate 110, such as the front electrode 141. In this case, the number of contact portions is much smaller than the number of contact portions having a circular, elliptic or polygonal shape.

The contact portion 151 collects charges, for example, holes moving from the side of the substrate 110, and transfers the collected charges to the rear electrode 155.

A plurality of contact portions 151 are formed on the substrate 110 so that a plurality of contact portions 151 are in contact with a plurality of rear electric field portions 172 having a conductivity higher than that of the substrate 110 due to impurity concentration higher than that of the substrate 110, The charge mobility is improved.

The rear electrode 155 is made of a conductive material such as aluminum (Al), but is not limited thereto.

A plurality of contacts 151 contacting the substrate 110 may contain only the components of the back electrode 155 or components of the back electrode 155 as well as components of the protection portion 190 and the substrate 110 have.

At this time, the second protective film 192 prevents the metal component such as aluminum (Al) contained in the rear electrode 155 from bonding with the silicon (Si) of the substrate 110 as described above, 155 prevent the passivation effect from decreasing due to the material contained in the passivation layer.

A plurality of rear bus bars 152 connected to the rear electrode 155 are disposed on the protective portion 190 where the rear electrode 155 is not located and extend in the same direction as the front bus bar 142, Shape. At this time, the plurality of rear bus bars 152 are opposed to the front bus bar 142 with the substrate 110 as a center.

These plurality of rear bus bars 152 collect charge that is transmitted from the rear electrode 155, similar to the plurality of front bus bars 142. Accordingly, the plurality of rear bus bars 152 may be made of a material having better conductivity than the back electrode 155. [ For example, at least one conductive material such as silver (Ag).

A plurality of rear bus bars 152 are also connected to external devices so that the charges (e.g., holes) collected by the plurality of rear bus bars 152 are output to an external device.

Unlike FIG. 1, in another example, a plurality of rear bus bars 152 may partially overlap with adjacent rear electrodes 155. In this case, the contact area with the rear electrode 155 is increased to decrease the contact resistance, so that the amount of charge transferred from the rear electrode 155 to the plurality of rear bus bars 152 increases. The backside electrode 155 may also be positioned on the protection portion 190 where the rear bus bar 152 is located and a plurality of rear bus bars 152 may be disposed on the substrate 110, And is positioned on the rear electrode 155 in a corresponding manner as opposed to the bar 142. In this case, since the rear electrodes 155 are disposed on the protective portions 190 irrespective of the positions of the plurality of rear bus bars 152, the process of forming the rear electrodes 155 becomes easier.

Further, in an alternative example, each rear-electrode bus bar 152 may be formed of a plurality of circular, elliptical, or polygonal shaped conductors arranged at regular or irregular intervals along the extending direction of each front bus bar 142 Lt; / RTI > In this case, expensive material consumption such as silver (Ag) for the rear electrode bus bar 152 is reduced, and manufacturing cost of the solar cell 11 is reduced.

The number of the plurality of rear bus bars 152 shown in FIG. 1 is also an example, and can be changed as needed.

The operation of the solar cell 11 according to this embodiment having such a structure is as follows.

When light is irradiated to the solar cell 11 and enters the semiconductor substrate 110 through the antireflection unit 130 and the emitter unit 121, electron-hole pairs are generated in the semiconductor substrate 110 by light energy . At this time, the reflection loss of the light incident on the substrate 110 is reduced by the anti-reflection unit 130, and the amount of light incident on the substrate 110 is increased.

These electron-hole pairs are separated from each other by the pn junction of the substrate 110 and the emitter section 121, and the electrons and the holes are separated from each other by, for example, an emitter section 121 having an n-type conductivity type and a p- Type substrate 110, respectively. Electrons migrating toward the emitter section 121 are collected by the front electrode 141 and the front bus bar 142 and are collected and transferred to the front bus bar 142. The holes moved toward the substrate 110 are collected by the adjacent Contact 151 and then collected by the rear bus bar 152. When the front bus bar 142 and the rear bus bar 152 are connected to each other by a wire, a current flows and is used as electric power from the outside.

Further, the emitter layer 121 is formed by the ion implantation method, and the sheet resistance value of the emitter layer 121 is increased, so that the loss amount of charges lost by the impurities in the emitter layer 121 is greatly reduced.

Next, an example of a manufacturing method of the solar cell 11 according to one embodiment of the present invention will be described with reference to FIGS. 3A to 3I.

First, as shown in FIG. 3A, a texturing process is performed on a crystalline semiconductor substrate 110 made of a single crystal, polycrystalline silicon, or the like, and a textured surface, which is an uneven surface, is formed on the front and back surfaces of the substrate 110. When the substrate 110 is made of monocrystalline silicon, the surface of the substrate 110 may be textured using a base solution such as KOH or NaOH. When the substrate 110 is made of polycrystalline silicon, HF or HNO ₃ May be used to texture the surface of the substrate 110.

At this time, the maximum diameter (a) and the height (b) of each concavity and convexity may be 5 占 퐉 to 15 占 퐉, and the longitudinal and transverse portions b / a of each concavity and convexity may be 0.2 to 2.

3, the maximum diameter (a) and the height (b) are the same as the sizes of the irregularities formed on the front surface and the rear surface of the substrate 110. However, b formed on the textured surface formed on the front and back surfaces of the plurality of concavo-convex substrates 110, respectively.

Since the textured surfaces having the same characteristics are formed on the front and rear surfaces of the substrate 110 in one process, the roughness per unit area of the textured surface formed on the front and back surfaces of the substrate 110 is the same.

In this example, the substrate 110 has a p-type conductivity type, but in an alternative example it may have an n-type conductivity type.

3B, ions of a pentavalent element or a trivalent element are implanted into only one surface of the substrate 110, for example, the surface of the substrate 110 by ion implantation, An impurity layer 120 is formed on the entire surface.

Since the n-type impurity is physically injected into the substrate 110, the impurity layer 120 has a surface resistance of several hundreds? / Sq., And the impurity layer 120 has a It can not perform the function as the emitter of the solar cell 11 because it is in an inactive state.

The substrate 110 having the impurity layer 120 is thermally treated in an oxygen (O ₂ ) atmosphere to form an impurity layer 120 doped with ions by ion implantation, (Si) lattice and the bonding between the impurity of the impurity layer 120 and the silicon or the impurity is performed so that the impurity layer 120 functions as the emitter layer 121, Heal the damaged area.

Then, the silicon oxide film formed on the surface of the substrate 110 by the combination of silicon (Si) and oxygen of the substrate 110 is removed by using a DHF (dilute HF) solution or the like. Therefore, the impurity layer 120 is changed to the emitter section 121 by the heat treatment process and the silicon (Si) lattice of the surface of the substrate 110 is etched by ions impinging on the surface of the substrate 110 in the ion implantation method. Defects such as dangling bonds present at and near the backside of the substrate 110 are converted into stable bonds. At this time, the emitter section 121 has a resistance of 60? / Sq. Lt; / RTI > to 120 ohms / sq.

That is, as the ions collide with the surface of the substrate 110, the damaged silicon lattice recrystallizes the silicon (Si) when heat of about 700 ° C to 900 ° C, which is around the recrystallization temperature of the substrate 110, A re-arrangement of the grid occurs. Thus, due to the heat treatment in such an oxygen atmosphere, the damaged silicon lattice is reorganized as a stable silicon lattice and the damaged silicon lattice is healed.

Since the emitter section 121 is formed only on the front surface of the substrate 110 as a desired surface when the emitter section 121 is formed by the ion implantation method as described above, the emitter section 121 formed on the undesired surface, ) Is eliminated. Therefore, manufacturing cost and manufacturing time of the solar cell 11 are reduced.

That is, when the emitter portion is formed on the substrate 110 using the heat diffusion method, the emitter portion is formed not only on the front surface of the substrate 110 but also on the side surface and the rear surface. Therefore, a process of removing the emitter portion formed on the back surface of the substrate 110 is required. Therefore, in this case, there is a need for a step of forming an etch stop layer on the portion of the emitter not desired to be etched (e.g., the front surface of the substrate), then removing the etch stop layer after the etching is completed. Further, the etching of the emitter portion formed on the back surface of the substrate 110 is not uniform. Even though the etch stopping film is used, the etchant penetrates the etch stopping film to damage the emitter portion formed on the entire surface of the substrate 110 or cause a change in characteristics. When the emitter portion of the desired portion is removed by exposing only the rear surface of the substrate 110 to the etchant without forming a separate etch stopper film, the back surface of the substrate 110 is exposed to the etchant The emitter portion of the undesired portion is also etched.

It is possible to form an emitter portion only on the front surface of the substrate 110 by forming a separate diffusion protecting film on the surface (e.g., rear surface) of the substrate that does not want to form the emitter portion before forming the emitter portion by the thermal diffusion method. In this case, however, the process of forming the diffusion barrier film and then removing the diffusion barrier film is required, resulting in an increase in manufacturing time and manufacturing cost of the solar cell.

However, as in the present example, since the ion implantation is performed only on the front surface of the desired substrate 110 by the ion implantation method which facilitates control of the ion implantation concentration and the implantation depth rather than the thermal diffusion method, thereby forming the emitter section 121, The formation process of the emitter layer 121 is performed at a very simple process and at a low cost compared to the conventional process.

In this case, since the removal process of the emitter portion formed on the rear surface of the substrate 110 is not necessary, the rear surface of the substrate 110 also maintains the textured surface same as the front surface.

Next, as shown in FIG. 3D, an emitter layer (not shown) is formed on the entire surface of the substrate 110 by using a film forming method such as plasma enhanced chemical vapor deposition (PECVD) or chemical vapor deposition (CVD) The anti-reflection part 130 is formed on the transparent substrate 121. At this time, the antireflective portion 130 may be made of silicon nitride (SiNx) having a refractive index of 2.0 to 2.1 and a thickness of about 70 nm to 80 nm.

3E and 3F, a first protective film 191 and a second protective film 192 are sequentially stacked on the rear surface of the substrate 110 by various film forming methods such as PECVD to form a protective portion 190 It completes. At this time, the first protective layer 191 may be made of silicon oxide (SiOx) or aluminum oxide (AlxOy), and the second protective layer 192 may be made of silicon nitride (SiNx).

When the first protective film 191 is made of silicon oxide (SiOx), the first protective film 191 may have a thickness of about 200 to 300 nm, and the first protective film 191 may be made of aluminum oxide (AlxOy) The first protective film 191 may have a thickness of about 30 nm to 70 nm.

Further, the second protective film 192 may have a thickness of about 40 nm to 80 nm.

Next, as shown in Fig. 3G, a paste containing silver (Ag) is applied to the corresponding portion of the antireflection portion 130 using a screen printing method, and then dried at about 120 DEG C to about 200 DEG C And the front electrode part pattern 40 are formed. The front electrode pattern 40 includes a front electrode pattern portion 41 and a front bus pattern portion 42 extending in a direction intersecting with each other.

Next, as shown in FIG. 3H, a paste containing aluminum (Al) is applied on the corresponding portion of the protective portion 190 using a screen printing method, and then dried at about 120 ° C. to about 200 ° C. to form a rear electrode pattern 55 are formed.

Next, as shown in FIG. 3I, a paste containing silver (Ag) is applied on the corresponding portion of the protective portion 190 using a screen printing method, and then dried to form a plurality of rear bus bar patterns 52 . 3I, a plurality of rear bus bar patterns 52 may be partially overlapped with the rear electrode patterns 55 and partially overlapped with the adjacent rear electrode patterns 55. In this case, as shown in FIG.

In the present embodiment, each of the rear bus bar patterns 52 has a stripe shape extending in one direction. Alternatively, circular, elliptical or polygonal patterns may be arranged at regular or irregular intervals in one direction.

The order of forming the front electrode pattern 40, the rear electrode pattern 55, and the rear bus bar pattern 52 can be changed.

3J, when a laser beam is selectively irradiated to a predetermined portion of the rear electrode pattern 55, the rear electrode pattern 55, the protective portion 190 at the lower portion thereof, and the substrate 110 are mixed with each other A molten mixture 153 is formed. In an alternative example, when each contact portion has a stripe shape, the irradiation region of the laser beam also has a stripe shape elongated in a predetermined direction.

At this time, the wavelength and the intensity of the laser beam are determined according to the material and thickness of the rear electrode pattern 55 and the protective portion 190 at the lower portion thereof.

The substrate 110 on which the rear electrode pattern 55, the plurality of rear bus bar patterns 52 and the front electrode pattern 40 are formed is then fired at a temperature of about 750 ° C to about 800 ° C, A front electrode portion 140 having a plurality of front electrodes 141 and a plurality of front bus bars 142, a rear electrode 155 having a plurality of contacting portions 151 and a plurality of rear bus bars 152 A rear electrode unit 150 and a plurality of rear electric power units 172 are formed to complete the solar cell 11 (FIGS. 1 and 2).

That is, when the heat treatment is performed, the anti-reflection portion 130 of the contact portion is penetrated by the front electrode pattern 40 by the lead (Pb) contained in the front electrode pattern 40, 40 are in contact with the emitter section 121 to form a front electrode section 140 including a plurality of front electrodes 141 and a front bus bar 142. At this time, the front electrode pattern portion 41 of the front electrode pattern 40 is a plurality of front electrodes 141, and the front bus bar pattern portion 42 is a plurality of front bus bars 142.

The portion 153 where the rear electrode pattern 55, the protective portion 190 at the lower portion thereof and the substrate 110 are mixed with each other makes contact with the substrate 110 to form a plurality of contact portions 151, And a plurality of rear bus bars 152 are formed by connecting the plurality of rear bus bar patterns 52 to the adjacent rear electrodes 155. [ As described above, when the plurality of contacts 151 are formed by using the laser beam, each contact 151 can include the components of the protection portion 190 and the substrate 110 as well as the components of the rear electrode 155.

  Further, during the heat treatment, chemical bonding is performed with the layers 121, 110, and 190 that are in contact with the metal components contained in the respective patterns 40, 55, and 52 to form the front electrode part 140 and the emitter part 121 The contact resistance between the plurality of contact portions 151 and the substrate 110 and between the rear electrode 155 and the rear bus bar 152 is reduced and the charge flow between them is improved.

 Aluminum (Al) contained in the rear electrode 151 diffuses toward the substrate 110 which is in contact with the contact portion 151 and is adhered to the substrate 110 in contact with the contact portion 151 in the heat treatment process. A plurality of rear electric fields 172 are formed in which the same impurity is a portion doped with a higher concentration than the substrate 110. [

The second protective film 192 and a part of the first protective film 191 under the first protective film 192 are removed in order to form a part of the rear surface of the substrate 110 A plurality of contact portions 151 can be formed.

3A to 3G, after the emitter 121, the reflection preventing part 130 and the protecting part 190 are formed on the substrate 110, a part of the protecting part 190 is removed Thereby forming a plurality of exposed portions that expose a part of the substrate 110. [ At this time, the exposed portion of the protective portion 190 may be formed using a dry etching method, a wet etching method, or a laser beam, and the shapes of the exposed portions may be a stripe shape in accordance with the shape of each contact portion 151, Circular, elliptical, or polygonal shape.

Next, a front electrode pattern 40 is formed on the antireflection portion 130 using a screen printing method, a rear electrode pattern 55 is formed on the protective portion 190 and the exposed substrate 110, A rear bus bar pattern 52 is formed on the protective portion 190 in contact with the rear electrode pattern 55.

Then, the front electrode part 140 connected to the emitter part 121, and the plurality of the protection parts 190 connected to the emitter part 121 by heat treatment of the substrate 110 having the patterns 40, 55, A rear electrode 155 having a plurality of contacts 151 connected to the substrate 110 through the exposed portion, a plurality of rear bus bars 152 connected to the rear electrode 155, and a plurality of contact portions 151 And a plurality of rear electric fields 172 are formed on the substrate 110. [ In this case, since the protective portion 190 is removed and a plurality of contact portions 151 are formed at the exposed portion of the substrate 110, the respective contact portions 151 may contain only components of the rear electrode 155.

Next, a solar cell 12 according to another embodiment of the present invention will be described with reference to FIGS. 4 and 5

The solar cell 12 shown in Figs. 4 and 5 has a structure similar to that of the solar cell 11 shown in Figs. 1 and 2, as compared with the solar cell 11 shown in Figs.

That is, the solar cell 12 includes a substrate 110, an emitter section 121 located only on the front surface of the substrate 110, which is a textured surface, which is an uneven surface by the texturing process, The protection unit 130 is also connected to the protection unit 190a and the emitter unit 121 which are located on the rear surface of the substrate 110 which is the textured surface and include the first and second protection films 191a and 192, A front electrode part 140 having a front electrode 141 and a plurality of front bus bars 142 and a rear electrode part 140 disposed on the protection part 190a and connected to the substrate 110, A back electrode unit 150 including an electrode 155 and a rear bus bar 152 and a plurality of contact electrodes 151 selectively located on the rear surface of the substrate 110 and connected to the plurality of contacts 151 of the rear electrode unit 150. [ And a rear electric section 172.

However, unlike the solar cell 11 of FIGS. 1 and 2, the solar cell 12 of the present embodiment further includes a front protective portion 193 between the emitter portion 121 and the anti-reflection portion 130. The first protective layer 191a of the protective portion 190a located on the rear surface of the substrate 110 is made of the same material as the front protective portion 193.

The first passivation layer 191a of the front passivation layer 193 and the rear passivation layer 190a located on the rear surface of the substrate 110 is formed of a thermal oxide film of silicon oxide (SiO ₂ ). At this time, the first protective film 191a of the front protective part 193, which is a thermal oxidation film, and the rear protective part 190a have a thickness of about 15 nm to about 30 nm.

Therefore, the passivation function of the substrate 110 is performed by the front surface protection part 193 located on the front surface of the substrate 110 as well as the reflection prevention part 130, so that defects existing on the surface of the substrate 110, The amount of charge lost by the transistor is greatly reduced.

The film quality of the thermal oxide film formed by the thermal oxidation method is superior to that of the silicon oxide film (SiOx) formed by the film formation method such as PECVD. Therefore, since the passivation function is performed on the front surface and the rear surface of the substrate 110 by the thermal oxidation method having excellent film quality, the passivation effect is further improved.

The first protective film 191a of the thermal oxide film and the first protective film 191a of the rear protective portion 190a are formed by implanting ions into the substrate 110 by the ion implantation method as described above with reference to FIGS. (Si) lattice caused in the substrate 110 by the ions impinging on the surface of the substrate 110 and the activation process of the impurity layer performed in the oxygen atmosphere.

Therefore, the first protective layer 191a of the front protective portion 193 and the rear protective portion 190a are not formed through a separate process but are formed during the heat treatment process performed in the oxygen atmosphere after the ion implantation process. Therefore, 191a are separately formed. Therefore, the manufacturing time of the solar cell 12 is shortened.

As described above, in the solar cell 12 according to the present embodiment, when the impurity layer is activated after the ion implantation to form the emitter layer 121, the surface of the substrate 110 damaged by the ion implantation process is treated, The first protective film 191a of the rear protective portion 190a and the front protective portion 193 which is a thermal oxide film generated during the treatment and having a good passivation effect, The amount of charge lost by the defect at the surface of the substrate 110 and in the vicinity thereof is further reduced. Therefore, the efficiency of the solar cell 12 of this example is further increased as compared with the solar cell 11 of FIGS. 1 and 2.

In the case where the rear protective portion 190a of the substrate 110 includes the first protective film 191a as a thermal oxide film and the second protective film 192 as a silicon nitride film, 1 protective film 191a.

At this time, the front electrode unit 140 collects charges moving through the front surface protection unit 193.

In this example, when the thickness of each of the first protective film 191a of the front surface protective portion 193 and the rear surface protective portion 190a is about 15 nm or more, damage of the damaged silicon lattice by the ion implantation method is more reliably treated, A passivation effect is obtained. When the thickness of each of the first protective film 191a of the front protective portion 193 and the rear protective portion 190a is about 30 nm or less, the heat treatment time is prevented from being unnecessarily increased and the damage of the silicon lattice is more reliably treated A more efficient passivation effect is obtained and the charge is moved more smoothly toward the front electrode part 140 through the front protective part 193 so that the charge of the front electrode part 140 is collected more stably.

A method of manufacturing such a solar cell 12 will be described with reference to Figs. 6A to 6G as well as Figs. 3A to 3H.

3A and 3B, a texturing process is performed on the substrate 110 to form a textured surface having uneven surfaces on the front and rear surfaces of the substrate 110, and the surface of the substrate 110 is subjected to ion implantation The impurity layer 120 is formed only on one surface, for example, only on the front surface.

6A, the substrate 110 on which the impurity layer 120 is formed is placed in a process chamber, and then the substrate 110 is heated to a temperature of about 700 ° C. to 900 ° C. in an oxygen (O ₂ ) atmosphere The impurity layer 120 is activated to form the emitter layer 121 and the damaged silicon lattice on the surface or the vicinity of the substrate 110 is treated by the ions impinging on the substrate 110 when the ion implantation is performed And defects such as dangling bonds present on and near the surface of the substrate 110 are converted into stable bonds to perform a passivation function.

That is, as the ions collide with the surface of the substrate 110, the damaged silicon lattice recrystallizes the silicon (Si) when heat of about 700 ° C to 900 ° C, which is around the recrystallization temperature of the substrate 110, A re-arrangement of the grid occurs. Thus, due to this heat treatment, the damaged silicon lattice is rearranged into a stable silicon lattice and the damaged silicon lattice is healed.

In this case, during the heat treatment process in the oxygen atmosphere, a thermal oxide film is formed on the front and rear surfaces of the substrate 110 exposed to the oxygen atmosphere during the heat treatment process, so that the front protective portion 193 and the substrate 110 A first protective film 191a is formed on the rear surface. At this time, the thickness of the thermal oxide films 193 and 191a may be about 15 nm to 30 nm.

3D, an antireflective portion 130 is formed on the front protective portion 193 of the substrate 110 by using a PECVD method or the like. Then, as shown in FIG. 3F, the substrate 110 The second protective layer 192 is formed on the first protective layer 191a on the rear surface of the second protective layer 190a (FIG. 6C). At this time, the order of forming the antireflective portion 130 and the second protective film 192 may be changed.

3G to 3I, a front electrode pattern 40 is formed on the antireflection portion 130 and a rear electrode pattern 55 and a rear bus bar pattern are formed on the rear protection portion 190a. (Fig. 6D to Fig. 6F).

3J, a laser beam is irradiated on the rear surface of the substrate 110 to form a portion 153 where the rear electrode pattern 55, the protective portion 190a at the lower portion thereof, and the substrate 110 are mixed with each other 6G), the substrate 110 having the patterns 55, 52, and 40 is heat-treated at a temperature of about 750 ° C. to about 800 ° C. to form a plurality of front electrodes 141 and a plurality of front bus bars A rear electrode part 150 having a plurality of rear bus bars 152 and a rear electrode 155 having a plurality of contact parts 151 and a rear electrode part 150 having a plurality of rear side bus bars 152, And a solar cell 12 is completed by forming the electric portion 172 (Figs. 4 and 5).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (22)

Implanting ions of a second conductivity type opposite to the first conductivity type on a first surface of a substrate having a first conductivity type by ion implantation to form an impurity layer;
Activating the impurity layer to form an emitter portion of the second conductivity type on a first side of the substrate;
Forming a front protective portion on the emitter portion;
Forming a rear protective part which is located on a second surface of the substrate opposite to the first surface and is composed of a first protective film formed on the substrate and a second protective film formed on the first protective film;
Forming an anti-reflection portion made of silicon nitride on the front protective portion; And
Forming a first electrode connected to the emitter portion and a second electrode selectively connected to the substrate through the first and second protective films;
Lt; / RTI >
Wherein the front protective part and the first protective film are simultaneously formed by the same process and are made of the same material and have the same thickness. The method of claim 1,
Wherein the first protective film comprises silicon oxide or aluminum oxide. The method of claim 1,
Wherein the front surface protection portion comprises silicon oxide. The method of claim 1,
Wherein the front protective portion and the first protective film are simultaneously formed by thermal oxidation. The method of claim 1,
Wherein the front protecting portion and the first protecting layer are formed in the step of forming the emitter portion by activating the impurity layer. The method of claim 5,
Wherein the step of activating the impurity layer to form the emitter layer is performed at a temperature of 700 ° C to 900 ° C. The method of claim 1,
Wherein the front protective portion and the first protective layer each have a thickness of 15 nm to 30 nm. The method of claim 1,
Wherein the second protective film is made of silicon nitride. The method of claim 1,
Wherein the first conductivity type is a p-type and the second conductivity type is an n-type. The method of claim 1,
Further comprising forming a texturing surface on the first and second surfaces of the substrate prior to forming the emitter portion. A substrate having a first conductivity type and opposing to each other and having first and second surfaces, each having a textured surface with a plurality of irregularities;
An emitter portion formed by ion implantation and located on a first surface of the substrate, the emitter portion having a second conductivity type opposite to the first conductivity type;
A first oxide film disposed on the emitter;
An antireflective portion positioned on the first oxide layer;
A second oxide film located on the second surface of the substrate;
A protective film disposed on the second oxide film;
A first electrode penetrating through the antireflection portion and the first oxide layer and electrically connected to the emitter portion;
A second electrode electrically connected to the substrate through the second oxide film and the protective film,
/ RTI >
Wherein the first oxide film and the second oxide film are made of the same material and have the same thickness. 12. The method of claim 11,
Wherein the second oxide film is a silicon oxide film or an aluminum oxide film. 12. The method of claim 11,
The emitter portion has a resistance of 60? / Sq. To 120 < RTI ID = 0.0 > ohm / sq. ≪ / RTI > 12. The method of claim 11,
Wherein the first and second oxide films each have a thickness of 15 nm to 30 nm. 12. The method of claim 11,
Wherein the protective film is made of silicon nitride. 12. The method of claim 11,
Wherein the protective film has a thickness of 40 nm to 80 nm. 12. The method of claim 11,
Wherein the reflection preventing portion is made of silicon nitride. 12. The method of claim 11,
Wherein the first conductivity type is a p-type and the second conductivity type is an n-type. 12. The method of claim 11,
And an electric field portion disposed on the substrate in contact with the second electrode. 12. The method of claim 11,
Wherein the first surface and the second surface have the same roughness. 12. The method of claim 11,
Wherein each of the plurality of irregularities has a maximum diameter and a height of 5 占 퐉 to 15 占 퐉. 12. The method of claim 11,
Each of the plurality of irregularities having an aspect ratio of 0.5 to 2. [

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