KR20120041340A - Method for manufacturing solar cell - Google Patents

Abstract

PURPOSE: A method for manufacturing a solar battery is provided to control shunt faults due to a first electrode by separately controlling doping depth of a part in which the first electrode is formed and a part in which the first electrode is not formed at one side of a substrate. CONSTITUTION: An emitter part(121) is located on the front side of a substrate(110). A back side field part(172) is located on the back side of the substrate. A back side electrode part(150) is located on the back side of the substrate. A front side electrode part is electrically and physically connected with the emitter part. The doping depth(D2) of a second part of the emitter part is deeper than the doping depth(D1) of a first area of the emitter part. A first area comprises a plurality of projection parts having a first height to width ratio. A second area comprises a plurality of projection parts having a second height to width ratio.

Description

Manufacturing method of solar cell {METHOD FOR MANUFACTURING SOLAR CELL}

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

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 the solar cell, a plurality of electron-hole pairs are generated in the semiconductor unit, and the generated electron-hole pairs are separated into electrons and holes charged by a photovoltaic effect, and the electrons are n-type. Move toward the semiconductor portion, and holes move toward the p-type semiconductor portion. The moved electrons and holes are collected by different electrodes connected to the n-type and p-type semiconductor parts, respectively, and are obtained by connecting these electrodes with wires.

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

Another technical problem to be achieved by the present invention is to reduce the defective rate of solar cells.

In the method of manufacturing a solar cell according to an aspect of the present invention, after placing a pattern mask having a different opening shape according to a position on a substrate, the first aspect ratio and the first aspect ratio may be respectively provided on the surface of the substrate of the first conductivity type by a single dry etching method. Forming a texturing surface having a plurality of protrusions having a second aspect ratio, implanting impurities into the substrate to form an emitter portion of a second conductivity type opposite to the first conductivity type, and the emitter portion; And forming a first electrode to be connected and a second electrode to be connected to the substrate, wherein the emitter portion includes a first region having a plurality of protrusions having the first aspect ratio and a plurality of second regions having the second aspect ratio. And a second region having a protrusion, wherein the first electrode is connected to the second region of the emitter portion.

The first aspect ratio is 1 to 1.5, the second aspect ratio is preferably 1.7 to 2.5.

The doping depth of the first region of the emitter portion may be smaller than the doping depth of the second region of the emitter portion.

The pattern mask includes a first portion having a plurality of first openings and a second portion having a second opening, wherein a portion of the substrate facing the first portion has a plurality of protrusions having the first aspect ratio. May be formed, and a plurality of protrusions having the second aspect ratio may be formed in a portion of the substrate facing the second portion.

Each of the plurality of first openings may have a shape of at least one of a circle, a polygon, and an oval.

The second opening may have a stripe shape extending in one direction.

The dry etching method is preferably a reactive ion etching method.

The method of manufacturing a solar cell according to the above feature may further include forming an anti-reflection portion on the emitter portion.

The forming of the first electrode and the second electrode may include applying a first electrode paste on a portion of the anti-reflective portion positioned on the second region of the emitter and then heat-treating the same to a first temperature. Applying a second electrode paste on the substrate positioned opposite to the protection unit, and then performing a heat treatment at a second temperature, and subjecting the substrate having the first electrode paste and the second electrode paste to a third temperature. It may include the step of heat treatment.

The first temperature and the second temperature may be the same.

The third temperature may be higher than the first temperature and the second temperature.

The first electrode paste may contain silver (Ag) and may further contain lead (Pb).

The second electrode paste may contain aluminum (Al).

According to this feature, since the doping depths of the portion where the first electrode is located and the portion that is not on one side of the substrate are different, the shunt defect caused by the first electrode is reduced, and the efficiency of the solar cell is improved.

1 is a partial perspective view of a solar cell 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 3E are views sequentially illustrating a method of manufacturing a solar cell according to one embodiment of the present invention.
4 is a schematic plan view of a pattern mask used in forming a texturing surface on the surface of a substrate in accordance with one embodiment of the present invention.
5A to 5C are diagrams illustrating a doping shape of the emitter part according to the shape of the protrusion when the emitter part is formed by the diffusion method.
6 is a graph showing a change in reflectivity according to the size of each protrusion according to the embodiment of the present invention.

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

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

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

A solar cell according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2.

1 and 2, a solar cell 11 according to an exemplary embodiment of the present invention has an incident surface (hereinafter, referred to as a 'front surface') that is a surface of a substrate 110 and a substrate 110 to which light is incident. The emitter region 121 positioned at the term "reflection", the antireflection portion 131 positioned at the emitter portion 121, the front electrode portion 140 connected to the emitter portion 121, and light are incident. The back surface field (BSF region) 172 positioned on a non-incidence surface (hereinafter referred to as a 'rear surface'), which is a surface of the substrate 110 positioned opposite to the incident surface. And a rear electrode part 150 positioned on the rear surface of the substrate 110.

The substrate 110 is a semiconductor substrate made of silicon of a first conductivity type, for example a p-type conductivity type. In this embodiment, the silicon is polycrystalline silicon, but may be single crystal silicon. When the substrate 110 has a p-type conductivity type, it contains impurities of trivalent elements such as boron (B), gallium, indium, and the like. Alternatively, the substrate 110 may be of an n-type conductivity type or may be made of a semiconductor material other than silicon. When the substrate 110 has an n-type conductivity type, the substrate 110 may contain impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb).

The front surface of this substrate 110 is textured to have a textured surface that is an uneven surface having a plurality of protrusions 21, 22.

In the present embodiment, the plurality of protrusions 21 and 22 may each have a maximum diameter a of several hundred nanometers, for example, from about 100 nm to about 800 nm, preferably from 300 nm to 600 nm. have. In the present embodiment, the plurality of protrusions 21 are protrusions formed on the surface of the substrate 110 on which the front electrode portion 140 is not located, and the aspect ratio (b / a) of each protrusion 21 is shown. Is about 1.0 to 1.5, and the plurality of protrusions 22 are protrusions formed on the surface of the substrate 110 on which the front electrode portion 140 is located, and the vertical and horizontal portions of each of the protrusions 22 are about 1.7 to 2.5. At this time, the height b of each of the first protrusions 21 is about 100 nm to 800 nm, preferably 300 nm to 600 nm, which is equal to the maximum diameter a, and the height b of each protrusion 22 is About 170 nm to 2000 nm.

For this reason, when the maximum diameters of the protrusions 21 and 22 are substantially constant, the protrusions 21 formed at portions where the aspect ratio of the protrusions 22 formed on the surface of the substrate 110 on which the front electrode portion 140 is located is not. Since the height is much larger than the aspect ratio, the height of the protrusion 22 is much larger than the height of the protrusion 21.

Since the size of the protrusions 21 formed on the surface of the substrate 110 in which the front electrode portion 140 is not located is small, such as hundreds of nanometers, the size of each protrusion 21 is small. The refractive index is continuously changed toward the substrate 110 from the portion in contact with the air (outer) in each of the micron-sized protrusions 21. That is, the upper side of each protrusion has a refractive index close to the refractive index of air, and the lower side has a refractive index close to the refractive index of silicon (Si), for example, the material of the substrate 110, and thus the plurality of refractive indexes are continuously changed. A layer stack effect such as stacking films occurs.

Accordingly, the wavelength band of light absorbed by the refractive index change according to the positional change of each protrusion 21 is also changed, thereby increasing the wavelength range of the light incident on the substrate 110. Accordingly, the reflectance of light in the wavelength range of about 300 nm to 1100 nm (eg, average weighted reflectance) by the texturing surface that textured the surface of the substrate 110 by dry etching according to the present embodiment. ] Has a low reflectivity of less than about 10%. This greatly improves the antireflection efficiency of the light of the solar cell 11 due to the texturing surface.

More specifically, as shown in FIG. 6, the size of each protrusion 21 is changed to the amount of chlorine gas Cl ₂ applied to form the texturing surface, thereby increasing the amount of chlorine gas Cl ₂ supplied. As the size of each protrusion 21 increases, the maximum diameter and height of each protrusion 21 increase, and conversely, as the supply amount of chlorine gas Cl ₂ decreases, the size of each protrusion 21 decreases, so that each protrusion 21 ), The maximum diameter and height become smaller. Referring to FIG. 6, the supply amount of chlorine gas (Cl ₂ ) when the average weighted reflectivity is about 10% or less is about 250 sccm to 1600 sccm, and at this time, the maximum diameter and height of each of the protrusions 21 formed are about 100 Nm to 800 nm. In addition, when the average weighted reflectivity is optimized to 5% or less, the supply amount of chlorine gas (Cl ₂ ) is approximately 400 sccm to 1400 sccm, wherein the maximum diameter and height of each of the protrusions 21 to be formed are approximately 300 nm to 600 nm.

When the maximum diameter and height of each protrusion is less than about 100 nm, the antireflection effect using the uneven surface cannot be effectively obtained because the textured surface is close to the flat surface. Therefore, when the maximum diameter and height of each protrusion is about 100 nm or more, the antireflection effect using the uneven surface is more stably and efficiently obtained. In addition, when the maximum diameter and height of each of the protrusions 21 is greater than about 800 nm, the uniformity of the protrusions 21 formed on the surface of the substrate 110 is lowered, and time for forming a textured surface and Consumption of process gas, such as chlorine gas (Cl ₂ ), increases, making control of the texturing surface forming process difficult. Therefore, when the maximum diameter and height of each protrusion 21 is about 800 nm or less, a plurality of protrusions 21 are formed more stably and uniformly without unnecessary waste of materials and an increase in processing time, thereby obtaining a more effective antireflection effect. .

In addition, as described above with reference to FIG. 6, when the maximum diameter and height of each protrusion 21 are approximately 300 nm to 600 nm, a more preferable antireflection effect is obtained.

By the texturing surface with the plurality of protrusions 21, 22, the antireflection efficiency of the solar cell 11 with respect to light is greatly improved, thereby increasing the amount of light incident into the solar cell 11.

The emitter part 121 is a region in which impurities of a second conductivity type, for example, an n-type conductivity type, which are opposite to the conductivity type of the substrate 110 are doped to the substrate 110, and the substrate is an incident surface. Located in front of the (110). Accordingly, the emitter portion 121 of the second conductivity type forms a p-n junction with the first conductivity type portion of the substrate 110.

As described above, since the front surface of the substrate 110 is a texturing surface having a plurality of protrusions 21 and 22, the surface of the emitter portion 121 doped with the substrate 110 also includes the plurality of protrusions 21 and 22. The uneven surface is provided, and the interface between the first conductive type portion of the substrate 110 and the emitter portion 121, that is, the bonding surface (that is, the pn bonding surface) of the substrate 110 and the emitter portion 121 is also a substrate ( There is a portion having an uneven surface similar to the surface of the substrate 110 due to the surface shape of the 110.

As described above, since the heights of the protrusions 21 and 22 vary depending on the position of the surface of the substrate 110, the emitter part 121 may include the first region having the first doping depth D1 and the second doping depth ( And a second region having D2). That is, the doping depths D1 and D2 of the emitter unit 121 also vary depending on the position of the substrate 110. At this time, the doping depth (D1, D2) means the depth from the surface to the bonding surface.

In other words, the doping depth D1 at each protrusion 21 is smaller than the doping depth D2 at each protrusion 22. As described above, since the doping depths D1 and D2 vary according to the position of the substrate 110, the impurity doping concentration of the emitter unit 121 also varies according to the doping depths D1 and D2. For example, the doping concentration of the impurity depends on the thickness, so that the thicker the thickness, the higher the doping concentration of the impurity. Therefore, in the present embodiment, the impurity doping concentration of the emitter portion 121 in the portion where the front electrode portion 140 is located is higher than the impurity doping concentration of the emitter portion 121 in the portion where the front electrode portion 140 is located. .

Due to the built-in potential difference due to the pn junction between the substrate 110 and the emitter portion 121, the electron-hole pairs, which are charges generated by light incident on the substrate 110, are electrons and holes. Separately, electrons move toward n-type and holes move toward p-type. Therefore, when the substrate 110 is p-type and the emitter portion 120 is n-type, the separated holes move toward the substrate 110 and the separated electrons move toward the emitter portion 121.

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

When the emitter portion 121 has an n-type conductivity type, the emitter portion 121 may be formed by doping the substrate 110 with impurities of a pentavalent element, and conversely, when the emitter portion 121 has a p-type conductivity type, The dopant may be formed by doping the substrate 110 with impurities.

The anti-reflection portion 130 on the emitter portion 121 may be formed of a silicon nitride layer (SiNx), a silicon oxide layer (SiOx), or the like. The anti-reflection unit 131 reduces the reflectivity of light incident on the solar cell 11 and increases the selectivity of a specific wavelength region, thereby increasing the efficiency of the solar cell 11. In the present embodiment, the anti-reflection unit 130 may have a single layer structure but may have a multilayered layer structure such as a double layer, and may be omitted as necessary.

The front electrode portion 140 is in contact with the second region of the emitter portion 121 and 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 electrically and physically connected to the emitter unit 121, and are spaced apart from each other and extend side by side in a predetermined direction. The front electrodes 141 collect electric charges, for example, electrons moved toward the emitter part 121.

The plurality of front bus bars 142 are electrically and physically connected to the emitter unit 121 and extend in parallel in a direction crossing the plurality of front electrodes 141.

In this case, the plurality of front bus bars 142 are positioned on the same layer as the plurality of front electrodes 141 and are electrically and physically connected to the corresponding front electrodes 141 at points crossing the front electrodes 141.

Thus, as shown in FIGS. 1 and 2, the plurality of front electrodes 141 have a stripe shape extending in the horizontal or vertical direction, and the plurality of front bus bars 142 extend in the vertical or horizontal direction. It has a stripe shape, the front electrode portion 140 is located in a grid form on the front surface of the substrate 110.

The plurality of front busbars 142 collects charges that are collected and moved by the plurality of front electrodes 141 as well as charges that travel from portions of the emitter portion 121 in contact.

Since each front busbar 142 must collect charges collected by the plurality of front electrodes 141 that cross each other and move them in a desired direction, the width of each front busbar 142 is greater than the width of each front electrode 141. Big.

The plurality of front busbars 142 are connected to an external device and output the collected charges (eg, electrons) to the external device.

The front electrode part 140 including 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).

1 and 2, the number of the front electrode 141 and the front busbar 142 positioned on the substrate 110 is only one example, and may be changed in some cases.

As such, due to the front electrode portion 140 electrically and physically connected to the emitter portion 121, the anti-reflection portion 130 is positioned on the emitter portion 121 where the front electrode portion 140 is not located.

As described above, since the front electrode 140 is in contact with the second region of the emitter portion 121 in which the doping depth is deeper than the first region of the emitter portion 121 and the doping concentration of impurities is greater, the first portion of the emitter portion 121 may be formed. The charge transfer efficiency between the two regions and the front electrode portion 140 is improved, and the occurrence of shunt defects due to the front electrode portion 140 is reduced.

That is, when the doping concentration of the impurity in the emitter portion 121 is low, the contact resistance increases, so that the amount of charge transfer from the emitter portion 121 to the front electrode portion 140 decreases, and the doping concentration of the impurity in the emitter portion 121 is reduced. When is high, defects such as dangling bonds occur on the surface of and near the emitter portion 121 due to impurities present in the emitter portion 121, and the front electrode portion 140 The movement of charges moving in the emitter portion 121 toward is hindered.

However, as described above, since the front electrode portion 140 is positioned in the second region of the emitter portion 121 having a high doping concentration of impurities, the charge transfer rate from the emitter portion 121 to the front electrode portion 140 is improved. . In addition, in the first region of the emitter portion 121 where the front electrode portion 140 is not located, the doping concentration of impurities is relatively low, so that defects caused by impurities are low, and the impurity doping concentration is relatively low. Since less movement disturbance occurs, the amount of charge loss due to defects on the surface of and near the first region of the emitter portion 121 decreases and the front electrode portion 140 from the first region of the emitter portion 121 is closer to the front electrode portion 140. The amount of charge transfer increases. As a result, the amount of charge transferred from the emitter unit 121 to the front electrode unit 140 increases, thereby improving the efficiency of the solar cell 11.

In addition, since the doping depth D2 of the second region of the emitter portion 121 where the front electrode portion 140 is located is larger than the doping depth D1 of the first region of the emitter portion 121, the front electrode portion ( The thickness of the emitter portion 121, which may be in contact with 140, increases, thereby increasing the contact margin of the front electrode portion 140. As a result, the shunt problem that the front electrode portion 140 penetrates the emitter portion 121 and contacts the first conductive type portion of the substrate 110 is reduced. Therefore, the leakage current and defective rate of the solar cell 11 are reduced, and the efficiency of the solar cell 11 is further improved.

In general, impurities of solid solubility or higher are implanted and impurities diffused into the substrate 110 have a concentration of inert impurities that do not normally bind to (dissolve) the material of the substrate 110, that is, silicon (Si). Increasingly, these inert impurities form a dead layer near the surface of the substrate 110, that is, near the surface of the emitter portion 121.

When the emitter portion 121 is formed inside the substrate 110 by a thermal diffusion method using a diffusion gas containing an impurity having a desired conductivity type, impurities may diffuse from the surface of the substrate 110 toward the inside of the substrate 110. Therefore, the closer the surface of the substrate 110, that is, the texturing surface, the higher the doping concentration of the impurities, the farther away from the texturing surface, the lower the doping concentration of the impurities. Therefore, since the impurity concentration increases toward the surface of the substrate 110, the inactive impurity concentration also increases toward the surface of the substrate 110, so that a dead layer is mainly formed near the surface of the substrate 110.

As such, dead layers in which inactive impurities are present cause loss of charge.

If the aspect ratio of each protrusion 21 located in the first region of the emitter portion 121 exceeds 1.5 and is higher than the maximum diameter of each protrusion 21 to increase the roughness of the texturing surface, each protrusion ( The thickness of the emitter portion 121 formed at the top portion rather than the periphery of 21) increases. Due to this, since the dead layer formation thickness at the top of each protrusion 21 is thicker than the periphery, the area of formation of the dead layer at the top of each protrusion 21 is increased than the periphery, so that the amount of charge loss in the dead layer is increased. Increases. In addition, since the height of each protrusion is high, the p-n junction depth at the top portion is greater than the p-n junction depth at another portion (eg, the peripheral portion), thereby increasing the loss of short wavelength light reaching the substrate 110.

In addition, when the aspect ratio of each protrusion 21 located in the first region of the emitter part 121 is less than 1, the height of each protrusion 21 is too low to obtain a stable reflection prevention effect of light.

However, in this embodiment, since the aspect ratio of each protrusion 21 located in the first region of the emitter portion 121 is maintained between 1 and 1.5, it reduces the charge loss due to the dead layer, and more efficient light due to the textured surface. The antireflection effect of is obtained.

The backside electric field 172 is a region in which impurities of the same conductivity type as the substrate 110 are doped to the substrate 110 at a higher concentration than the substrate 110, for example, a P + region.

The potential barrier is formed due to the difference in the impurity concentration between the first conductive region and the backside electric field 172 of the substrate 110, thereby preventing electrons from moving toward the backside electric field 172, which is the movement direction of the hole. The hole movement toward the rear electric field 172 becomes easier. Accordingly, the back side electric field 1720 reduces the amount of charge lost due to the recombination of electrons and holes in and around the back side of the substrate 110 and accelerates the movement of the desired charge (eg, holes). Increase the amount of charge transfer to

The rear electrode unit 150 includes a rear electrode 151 and a plurality of rear bus bars 152 connected to the rear electrode 151.

The rear electrode 151 is in contact with the rear electric field unit 172 positioned at the rear of the substrate 110, and is substantially positioned over the entire rear surface of the substrate 110 except for the portion where the rear bus bar 152 is positioned. In an alternative example, the back electrode 151 may not be located at the back edge portion of the substrate 110.

The rear electrode 151 contains a conductive material such as aluminum (Al).

The back electrode 151 collects charge, for example, holes, moving from the back field 172.

In this case, since the rear electrode 151 is in contact with the rear electric field unit 172 having a higher impurity concentration than the substrate 110, the contact resistance between the substrate 110, that is, the rear electric field unit 172 and the rear electrode 151 is increased. This decrease improves the charge transfer efficiency from the substrate 110 to the back electrode 151.

The plurality of rear bus bars 152 are positioned on the rear surface of the substrate 110 where the rear electrode 151 is not located and are connected to the adjacent rear electrode 151.

In addition, the plurality of rear bus bars 152 may face the plurality of front bus bars 142 with respect to the substrate 110.

The plurality of rear busbars 152 collects charges transferred from the rear electrode 151, similar to the plurality of front busbars 142.

The plurality of rear busbars 152 are also connected to an external device, and the charges (eg, holes) collected by the plurality of rear busbars 152 are output to the external device.

Since the plurality of rear busbars 152 have to output the electric charges transferred from the rear electrode 151 to an external device, the plurality of rear busbars 152 may be made of a material having a better conductivity than the rear electrode 151, for example, silver (Ag). At least one conductive material, such as

In an alternative example, the rear electrode 151 may also be located in the rear portion of the substrate 110 where the rear busbar 152 is located, in which case the plurality of rear busbars 152 are centered on the substrate 110. In order to face the plurality of front busbars 142 to correspond to the rear electrode 151 is located. In this case, in some cases, the rear electrode 151 may be located on the entire rear surface of the rear surface except for the edge portion of the rear surface.

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

When light is irradiated onto the solar cell 11 and incident on the emitter portion 121, which is a semiconductor portion, and the substrate 110 through the anti-reflection portion 130, electron-hole pairs are generated on the substrate 110 of the semiconductor by light energy. . At this time, the reflection loss of the light incident on the substrate 110 by the texturing surface of the substrate 110 and the anti-reflection portion 130 is reduced, thereby increasing the amount of light incident on the substrate 110.

These electron-hole pairs are separated from each other by the pn junction of the substrate 110 and the emitter portion 121 so that the electrons and holes are, for example, the emitter portion 121 having the n-type conductivity type and the p-type conductivity. Respectively move toward the substrate 110 having the type. As such, the electrons moved toward the emitter unit 121 are collected by the plurality of front electrodes 141 and the plurality of front busbars 142, move along the plurality of front busbars 142, and toward the substrate 110. The moved holes are collected by the adjacent rear electrode 151 and the plurality of rear busbars 152 and move along the plurality of rear busbars 152. When the front bus bar 142 and the rear bus bar 152 are connected with a conductive wire, a current flows, which is used as power from the outside.

At this time, since the doping depth D2 of the region of the emitter portion 121 in contact with the front electrode portion 140 on the front surface of the substrate 110 is larger than the doping depth D1 of the other region, the emitter portion 121 is formed. The amount of charge transfer to the front electrode portion 140 increases and the risk of shunt generation decreases, thereby improving the efficiency of the solar cell 11 and lowering the defective rate of the solar cell 11.

Next, a method of manufacturing the solar cell 11 according to an embodiment of the present invention will be described with reference to FIGS. 3A to 3E, 4, and 5.

First, as illustrated in FIG. 3A, a front surface of the substrate 110 that is one surface of the exposed substrate 110 using a dry etching method such as reactive ion etching (RIE), for example, an incident surface. Is etched to form a texturing surface having a plurality of protrusions 21, 22.

In this case, the substrate 110 to be etched is disposed in the process chamber, and the pattern mask 80 having the plurality of openings 81 and 82 formed thereon is positioned on the substrate 110, and then a process gas is injected to the substrate 110. A texturing surface with a plurality of protrusions 21, 22 is formed on the face.

As a result, texturing surfaces having different aspect ratios of the protrusions 21 and 22 are formed according to the position of the substrate 110. For example, the aspect ratio of each protrusion 21 is about 1 to 1.5, and the aspect ratio of each protrusion 22 is about 1.7 to 2.5. Therefore, when the maximum diameter a of each protrusion 21 and 22 is about 100 nm to 800 nm, the height b of each protrusion 21 is about 100 nm to 800 nm equal to the maximum diameter a. The height b of each protrusion 22 may be about 170 nm to 2000 nm.

At this time, the surface of the pattern mask 80 adjacent to the substrate 110, that is, the distance from the lower surface of the pattern mask 80 to the surface of the substrate 110 before the texturing surface is formed may maintain about 3 mm to 30 mm. have.

When the distance between the lower surface of the pattern mask 80 and the surface of the substrate 110 is about 3 mm or more, the shape of the pattern mask 80 formed by the plurality of openings 81 and 82 is formed on the surface of the substrate 110. By further reducing the transfer problem, a plurality of protrusions 21 and 22 having different aspect ratios are formed according to the position of the substrate 110. In addition, when the distance between the lower surface of the pattern mask 80 and the surface of the substrate 110 is about 30 mm or less, the pattern of the pattern mask 80 by the plurality of openings 81 and 82 may be used. According to the position, the plurality of protrusions 21 and 22 having different aspect ratios can be more stably formed.

As shown in FIG. 4, the pattern mask 80 is divided into a first portion having a plurality of first openings 81 and a second portion having a plurality of second openings 82. In this case, each of the plurality of first openings 81 has a circular cross-sectional shape having a predetermined diameter, and the plurality of second openings 82 have a predetermined width w1 and w2 and have a stripe shape extending in the corresponding direction. Have Thus, each second opening 82 has a rectangular cross-sectional shape. In FIG. 4, the spacing between two adjacent first openings 81 may be constant but not, and the plurality of first openings 81 may have diameters of at least two different sizes.

Unlike FIG. 4, in an alternative example, the opening 181 may have a polygonal or oval cross-sectional shape, such as a triangle or a square, instead of a circular cross-sectional shape, and the first portion in which the plurality of openings 181 are formed may have a plurality of shapes. A plurality of openings having a cross-sectional shape of may be mixed.

The plurality of second openings 82 has a plurality of openings 81 having a first width w1 and a plurality of second openings 81 having a width larger than the first width w1.

A plurality of protrusions 21 having an aspect ratio of about 1 to 1.5 is formed in the surface portion of the substrate 110 corresponding to the first portion of the pattern mask 80 in which the plurality of openings 81 are positioned, and the plurality of openings 82 A plurality of protrusions 22 having an aspect ratio of about 1.7 to about 2.5 are formed in the surface portion of the substrate 110 corresponding to the second portion of the pattern mask 80 in which the) is located.

In this case, each protrusion may be formed according to at least one of a diameter or a shape of the first opening 81, a gap between two adjacent first openings 81, and a distance between the bottom surface of the pattern mask 80 and the surface of the substrate 110. The aspect ratios of 21 and 22 may vary.

In the present embodiment, the substrate 110 is a substrate made of p-type polycrystalline silicon, but is not limited thereto, and may be a substrate made of single crystal or amorphous silicon, and the conductivity type of the substrate 110 may also be n-type.

Next, as shown in FIG. 3B, a material containing impurities of pentavalent elements such as phosphorus (P), arsenic (As), antimony (Sb), and the like, for example, POCl ₃ or H ₃ PO in the substrate 110. ₄ and the like are heat-treated at a high temperature to diffuse impurities of the pentavalent element onto the substrate 110 to form the emitter portion 121 on the entire surface of the substrate 110, that is, the front, rear, and side surfaces thereof. Unlike the present embodiment, when the conductivity type of the substrate 110 is n-type, a material containing an impurity of trivalent element, for example, B ₂ H ₆ is heat-treated or laminated at a high temperature to the entire surface of the substrate 110. The p-type emitter portion 121 may be formed. Subsequently, an oxide containing phosphorus (phosphorous silicate glass, PSG) or boron containing silica (boron silicate glass, BSG) generated as the p-type impurity or the n-type impurity diffuses into the substrate 110 is fluorinated ( HF) or the like.

As such, when the emitter portion 121 is formed by the thermal diffusion process, the diffusion depth of impurities in the texturing surface of the substrate 110 depends on the shape of the protrusions 21 and 22 formed on the substrate 110, that is, the aspect ratio. Different.

When the impurity diffusion process for forming the emitter portion 121 is performed, as shown in FIG. 5, the impurity diffuses into the substrate 110 in a circular shape along the surface of the substrate 110 at one point. Therefore, when the aspect ratio of each protrusion is large, since the width variation in each protrusion is large, the diffusion region of impurities overlaps, and the portion doped with impurities increases in each protrusion, so that most of the protrusions are doped with impurities (Fig. 5 (a)]. However, when the aspect ratio of each protrusion is small, since the width variation in each protrusion is small, the area where the impurity diffusion overlaps is reduced, and impurities are mainly doped only along the surface of the protrusion (Fig. 5 (c) )]. In Figs. 5A to 5B, L1-L3 is a p-n junction surface.

Therefore, as the aspect ratio of the protrusion increases, the doping thickness of the emitter portion 121 increases, so that the first doping of the first region of the emitter portion 121 in which the plurality of protrusions 21 having the aspect ratio of about 1 to 1.5 is formed. The second doping depth D2 of the second region of the emitter portion 121 in which the plurality of protrusions 22 having an aspect ratio of about 1.7 to 2.5 is formed larger than the depth D1.

The first region of the emitter portion 121 having the first doping depth D1 faces the first portion of the pattern mask 80 having the plurality of first openings 81, and the second doping depth D2. The second region of the emitter portion 121 having the second surface facing the second portion of the pattern mask 80 having the plurality of first openings 82. As such, in the present exemplary embodiment, the plurality of protrusions having different aspect ratios controls the amount of etching gas that passes through the pattern mask 80 and reaches the surface of the substrate 110 to control the amount of etching gas having different aspect ratios according to positions. 21, 22).

As described above, the patterning surface 80 having the protrusions 21 and 22 having different aspect ratios according to the position of the substrate 110 is formed on the substrate 110 by using the pattern mask 80 having a different pattern shape according to the position of the substrate 110. In an alternative example, however, a portion of the texturing surface may be removed to form a plurality of protrusions 21, 22 having different aspect ratios.

That is, the reactive ion etching method forms a texturing surface having a plurality of protrusions having an aspect ratio of about 1.7 to 2.5 on the entire surface of the substrate 110, and then selectively forms an etch stop layer of silicon oxide or the like on the texturing surface. Then, the entire surface of the substrate 110 is etched by a dry etching method or a wet etching method. As a result, a portion of the texturing surface of the substrate 110 where the etch stop layer is not exposed and exposed to the etching gas or the etchant is not etched and the texturing surface of the substrate 110 protected by the etch stop layer is not etched.

Thus, a portion of the plurality of protrusions formed on the textured surface on which the etching is performed is etched. In this case, since the amount of etching at each protrusion is not constant, and the top portion is more etched than the other portions, the aspect ratio of each protrusion formed on the etched texturing surface is reduced to about 1 to 1.5. The aspect ratio of each protrusion formed on the unetched texturing surface is maintained between about 1.7 and 2.5.

As a result, a plurality of protrusions 21 and 22 having different aspect ratios may be formed according to the position of the substrate 110.

Next, as shown in FIG. 3C, the antireflection portion 130 is formed on the emitter portion 121 formed on the entire surface of the substrate 110 using plasma enhanced chemical vapor deposition (PECVD) or the like.

Next, as shown in FIG. 3D, the front electrode paste containing silver (Ag) and glass frit is printed on the corresponding portion of the anti-reflection portion 130 and dried by using a screen printing method. The front electrode part pattern 40 is formed. Glass frit includes lead (Pb) and the like.

In this case, the front electrode pattern 40 includes a portion 41 for the plurality of front electrodes and a portion 42 for the plurality of front bus bars. In the present embodiment, the front electrode portion pattern 40 is positioned on the second region of the emitter portion 121, that is, the region in which the plurality of protrusions 22 having an aspect ratio of about 1.7 to 2.5 are formed. At this time, the portion 41 for the plurality of front electrodes is a texturing surface of the substrate 110 formed by the second opening 82 having the first width w1 of the second openings 82 of the pattern mask 80. The portion 42 located above and for the plurality of front side busbars is a texturing of the substrate 110 formed by the second opening 82 having a second width w2 of the second openings 82 of the pattern mask 80. Located on the surface

Next, as shown in FIG. 3E, the paste for back electrode containing aluminum (Al) is selectively printed on the rear surface of the substrate 110 by screen printing and then dried to emitter parts formed on the rear surface of the substrate 110 ( The rear bus pattern 51 is formed on the rear electrode pattern 51, and the rear bus bar paste containing silver (Ag) is selectively printed on the rear of the substrate 110 by screen printing and then dried to dry the rear bus bar pattern 52. To form a rear electrode pattern 50.

At this time, the drying temperature of these patterns 40, 51, 52 may be about 120 ℃ to about 200 ℃, the order of forming the patterns 40, 51, 52 can be changed.

Then, the substrate 110 on which the front electrode part pattern 40 and the back electrode part pattern 50 are formed is subjected to a heat treatment process at a temperature of about 750 ° C. to about 800 ° C., whereby the first region of the emitter part 121 is formed. The front electrode portion 140 and the substrate which are in contact with the second region of the emitter portion 121 having a larger doping depth D2 of impurity and have a plurality of front electrodes 141 and a plurality of front bus bars 142. A rear electrode unit 171 is formed in the rear electrode unit 150 having the rear electrode 151 electrically connected to the 110 and the rear bus bar 152, and the substrate 110 in contact with the rear electrode 151. do.

That is, by the heat treatment process, the lead electrode pattern 40 is penetrated by the lead (Pb) contained in the front electrode portion pattern 40, and the emitter portion penetrates through the anti-reflection portion 130 at the contact portion. A plurality of front electrodes 141 and a plurality of front electrode bus bars 142 contacting 121 are formed to complete the front electrode 140. At this time, the front electrode pattern 41 of the front electrode part pattern 40 becomes the plurality of front electrodes 141, and the front bus bar pattern 42 becomes the plurality of front electrode bus bars 142.

As such, the second region of the emitter portion 121 having the relatively large doping depth D2 and the front electrode portion 140 contact with each other on the front surface of the substrate 110, and thus, the second region of the emitter portion 121. The contact margin of the front electrode part 140 that can be contacted is increased to reduce the occurrence of shunt defects penetrating the emitter part 121 during the penetrating operation of the front electrode part pattern 40. In addition, due to the increase in the doping depth D2, the contact resistance between the emitter portion 121 and the front electrode portion 140 decreases, thereby increasing the amount of charge transfer from the emitter portion 121 to the front electrode portion 140. For this reason, the efficiency of the solar cell 11 is improved.

In addition, by the heat treatment process, the rear electrode pattern 51 and the rear bus bar pattern 52 of the rear electrode part pattern 50 are formed of the rear electrode 151 and the plurality of rear bus bars 152, respectively, The aluminum (Al) included in the back electrode pattern 51 of the electrode part pattern 50 is diffused into the substrate 110 not only through the emitter part 121 formed on the back of the substrate 110 but also beyond the substrate 110. A rear electric field part 172 which is an impurity part having a higher impurity concentration than the substrate 110 is formed therein. As a result, the rear electrode 151 is in contact with the rear electric field unit 172 and electrically connected to the substrate 110.

  In the heat treatment process, the contact resistance is reduced by chemical coupling between the metal components contained in the patterns 40 and 50 and the layers 121 and 110 in contact with each other, thereby improving charge transfer efficiency and increasing current flow.

Then, the solar cell 1 is completed by performing an edge isolation process of removing the emitter portion 121 doped to the side surface of the substrate 110 by using a laser beam or an etching process. . However, the timing of the side separation process can be changed as necessary.

In the present embodiment, the emitter portion 121 formed on the rear surface of the substrate 110 is not separately removed, but in an alternative example, the emitter portion 121 formed on the rear surface of the substrate 110 is formed before forming the rear electrode pattern 50. A separate process for removing the emitter portion 121 may be performed.

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

Claims (14)

A texturing surface having a plurality of protrusions having a first aspect ratio and a second aspect ratio, respectively, on a surface of a substrate of a first conductivity type after positioning a pattern mask having a different opening shape depending on the position on the substrate. Forming a step,
Implanting impurities into the substrate to form an emitter portion of a second conductivity type opposite to the first conductivity type, and
Forming a first electrode connected to the emitter unit and a second electrode connected to the substrate
Including,
The emitter portion includes a first region having a plurality of protrusions having the first aspect ratio and a second region having a plurality of protrusions having the second aspect ratio,
The first electrode is connected to the second region of the emitter portion.
Method for manufacturing a solar cell. In claim 1,
The first aspect ratio is 1 to 1.5, the second aspect ratio is 1.7 to 2.5 of the manufacturing method of the solar cell. The method of claim 1 or 2,
And a doping depth of the first region of the emitter portion is smaller than a doping depth of the second region of the emitter portion. In claim 1,
The pattern mask includes a first portion having a plurality of first openings and a second portion having a second opening,
An aspect in which a plurality of protrusions having the first aspect ratio are formed at a portion of the substrate facing the first portion, and a plurality of protrusions having the second aspect ratio are formed at a portion of the substrate facing the second portion Method for producing a battery. In claim 4,
Each of the plurality of first openings has a shape of at least one of a circle, a polygon, and an oval. In claim 4,
The second opening has a stripe shape extending in one direction. In claim 1,
The dry etching method is a method of manufacturing a solar cell is a reactive ion etching method. In claim 1,
And forming an anti-reflection portion on the emitter portion. 9. The method of claim 8,
The first electrode and the second electrode forming step,
Applying a paste for a first electrode on a portion of the anti-reflective portion positioned on the second region of the emitter portion, and then heat-treating at a first temperature;
Applying a second electrode paste on the substrate positioned opposite to the anti-reflection portion, and then heat-treating at a second temperature; and
And heat-treating the substrate having the first electrode paste and the second electrode paste at a third temperature. In claim 9,
And the first temperature and the second temperature are the same. The method of claim 9 or 10,
And the third temperature is higher than the first temperature and the second temperature. In claim 9,
The method for manufacturing a solar cell, wherein the first electrode paste contains silver (Ag). In claim 11,
The method for manufacturing a solar cell, wherein the first electrode paste further contains lead (Pb). In claim 9,
The second electrode paste contains aluminum (Al).

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