KR101307204B1 - Solar cell and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a solar cell and a manufacturing method thereof.
One example of a solar cell according to the present invention includes a substrate doped with impurities of a first conductivity type; An emitter portion positioned in front of the substrate and doped with impurities of a second conductivity type opposite to the first conductivity type to form a pn junction with the substrate; A rear field unit positioned at a rear side of the substrate and doped with a higher concentration of impurities of the first conductivity type than the substrate; A first electrode part electrically connected to the emitter part; And a second electrode part electrically connected to the rear electric field part, wherein the rear electric field part includes a first uneven part having a size of 2 μm or less.

Description

SOLAR CELL AND MANUFACTURING METHOD THEREOF

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 the solar cell, electrons and holes are generated in the semiconductor, and charges generated by the pn junctions move to the n-type and p-type semiconductors, respectively, so that the electrons move toward the n-type semiconductor portion, and the holes are p-type semiconductors. Move to the 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.

It is an object of the present invention to provide a solar cell and a method of manufacturing the same that improve the efficiency of the solar cell and reduce the manufacturing cost.

One example of a solar cell according to the present invention includes a substrate doped with impurities of a first conductivity type; An emitter portion disposed in front of the substrate and doped with impurities of a second conductivity type opposite to the first conductivity type to form a p-n junction with the substrate; A rear field unit positioned at a rear side of the substrate and doped with a higher concentration of impurities of the first conductivity type than the substrate; A first electrode part electrically connected to the emitter part; And a second electrode part electrically connected to the rear electric field part, wherein the rear electric field part includes a first uneven part having a size of 2 μm or less.

Here, the rear of the electric field portion further includes a second uneven portion having a larger size than the first uneven portion, the first uneven portion may be formed on the surface of the second uneven portion.

In addition, the protruding height of the first uneven portion may be smaller than the protruding height of the second uneven portion. For example, the protruding height of the first uneven portion may be 2 μm or less, and the protruding height of the second uneven portion may be 5-15 μm.

In addition, the thickness of the second electrode part may be between 35 μm and 45 μm, and the thickness of the rear electric field part may be between 5 μm and 9 μm.

In addition, an example of the solar cell manufacturing method according to the present invention comprises the steps of forming a first uneven portion on the back surface of the substrate having a first conductivity type; Forming an emitter portion including impurities of a second conductivity type opposite to the first conductivity type on the entire surface of the substrate; And diffusing the same impurity as the first conductivity type into the rear surface of the substrate having the first uneven portion formed at a higher concentration than the substrate to form a rear electric field portion.

The first uneven portion may be formed by reactive ion etching (RIE).

In addition, before forming the first uneven portion, anisotropic etching may be further performed on the rear surface of the substrate to form a second uneven portion having a larger size than the first uneven portion on the rear surface of the substrate.

Here, the alkaline solution may include potassium hydroxide (KOH) or sodium hydroxide (NaOH).

In addition, applying a first paste for forming a first electrode portion on the entire surface of the substrate; And applying a second paste to form a second electrode part on a rear surface of the substrate.

Here, when the first paste and the second paste are heat treated to form the first electrode portion and the second electrode portion, the backside electric field portion may be formed at the same time.

The solar cell according to the present invention includes the first uneven portion having a size of 2 μm or less on the rear surface of the rear electric field part, thereby improving the efficiency of the solar cell and at the same time reducing the manufacturing cost.

1 to 3 are views for explaining a solar cell according to an embodiment of the present invention.
4 is a view for explaining the relationship between the thickness of the rear electric field and the open voltage.
FIG. 5 is a diagram illustrating an optimized thickness of a backside electric field according to photoelectric conversion efficiency of a solar cell.
6A to 6G are diagrams for explaining an example of a solar cell manufacturing method according to the present invention, which is viewed from the side of the solar cell along the line II-II of FIG.

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 is enlarged to clearly represent the layers and regions. When a part of a layer, film, region, plate, etc. is said to be "on top" of another part, this includes not only being in "top directly above" the other part but also in the middle of another part. When a part is "just above" another part, there is no other part in the middle, and when a part is formed "overall" on another part, it is formed only on the entire surface of the other part. It does not mean that some of the edges are not formed.

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

1 to 3 are views for explaining a solar cell according to an embodiment of the present invention.

Specifically, Figure 1 is a perspective view of a portion of a solar cell according to the invention, Figure 2 is a side view of the solar cell according to the invention according to the line II-II in Figure 1, Figure 3 is in Figure 1 FIG. 4 is a diagram for comparing and comparing the protrusions formed on the emitter unit illustrated with the protrusions formed on the rear electric field unit.

In FIG. 3, (a) is an enlarged view of a portion A shown in FIG. 2, and is an example of a plurality of second uneven portions P2 formed on the front surface of the emitter unit 120. An enlarged view of a portion B shown in FIG. 2 illustrates an example of the plurality of second uneven parts P2 and the first uneven parts P1 formed on the rear surface of the rear electric field part 170.

In the following embodiment, a solar cell in which the first electrode part 150 and the second electrode part 160 having different polarities are formed on different surfaces of the substrate 110 will be described as an example. The unit 150 and the second electrode unit 160 may be applied to a solar cell formed on the same surface of the substrate 110, respectively.

Examples of such a solar cell 1 include a substrate 110, an emitter portion 120 positioned on the front surface of the substrate 110, an antireflection portion 130 positioned on the front surface of the emitter portion 120, and a substrate. Located in the back surface field (BSF, 170) located on the rear of the 110, the first electrode portion 150 located in the upper front of the emitter unit 120 and the upper portion of the rear of the substrate 110 The second electrode unit 160 may be included.

The substrate 110 may be formed by doping impurities of a first conductivity type, for example, impurities of a p-type conductivity.

When the substrate 110 has a p-type conductivity type, impurities of trivalent elements such as boron (B), gallium (Ga), and indium (In) may be doped into the substrate 110. 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, the substrate 110 may be formed by doping the substrate 110 with impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb). Can be.

When light is incident on the substrate 110, electrons and holes are generated due to the energy of the incident light.

The substrate 110 may be formed of at least one of amorphous silicon, single crystal silicon, and polycrystalline silicon. For example, the substrate 110 may be made of only amorphous silicon, single crystal silicon, or polycrystalline silicon, or may be a mixture of single crystal silicon and polycrystalline silicon.

Hereinafter, the case where the substrate 110 is made of single crystal silicon will be described as an example.

The rear surface of the substrate 110 according to the present invention may include a first uneven portion having a size of 2㎛ or less.

In addition, the rear surface of the substrate 110 according to the present invention may further include a second uneven portion having a larger size than the first uneven portion along with a first uneven portion having a size of 2 μm or less.

Here, the second uneven portion having a relatively large size may be formed on the front and rear surfaces of the substrate 110 in the process of texturing the front and rear surfaces of the substrate 110, and the first uneven portion having the relatively small size may be formed of the substrate ( It may be formed by performing a reactive ion etching on the back of the (110).

Therefore, when the substrate 110 is made of single crystal silicon, an anisotropic etching is performed on the rear surface of the substrate 110 to form a relatively large second uneven portion, and thereafter, reactive ion etching is performed to perform the second uneven portion. The first uneven portion can be formed on the surface.

However, it is also possible that the second uneven portion is omitted in the present invention. More specifically, when the substrate 110 is made of polycrystalline silicon, unlike when the substrate 110 is made of single crystal silicon, the second uneven portion having a relatively large size may be formed even if anisotropic etching is performed on the rear surface of the substrate 110. It is possible to maintain a flat surface without being formed, and when reactive ion etching is performed, first uneven portions having a size of 2 μm or less may be formed on the surface of the flat surface.

As such, when the rear surface of the substrate 110 includes a first uneven portion having a size of 2 μm or less, the rear surface area of the substrate 110 may be further increased.

As such, when the first uneven portion is formed on the rear surface of the substrate 110, the thickness of the rear electric field portion 170 formed on the rear surface of the substrate 110 may be increased, thereby improving efficiency of the solar cell. .

More specifically, the rear electric field unit 170 is formed by diffusion of impurities from the rear surface of the substrate 110 to the inside. When the first uneven portion is formed on the rear surface of the substrate 110, the rear surface area of the substrate 110 is formed. As a result, impurities diffused from the rear surface of the substrate 110 into the substrate 110 may be further increased.

Accordingly, in the case where the rear electric field unit 170 is formed through the heat treatment process for the same time, the thickness of the rear electric field unit 170 is increased more significantly than in the case where the first uneven portion is formed on the rear surface of the substrate 110. You can.

As such, when the rear surface area of the substrate 110 is relatively increased, the thickness of the rear electric field unit 170 formed on the rear surface of the substrate 110 is further increased even if the thickness of the second electrode unit 160 is not increased. It can form thickly and can further improve the photoelectric conversion efficiency of a solar cell.

More specifically, when the thickness of the rear electric field unit 170 becomes relatively thicker, the open voltage Voc of the solar cell is further increased under the influence of the electric field of the rear electric field unit 170. In this case, the photoelectric conversion efficiency of the solar cell is further increased.

However, in order to increase the thickness of the rear electric field unit 170 in this manner, the amount of impurities doped on the rear surface of the substrate 110 should be greater. As described above, in order to increase the amount of impurities doped on the rear surface of the substrate 110, an impurity doping time must be increased, and the thickness of the second electrode unit 160 that supplies the impurities to the rear surface of the substrate 110 is also increased. There is a problem that must be large.

However, when the doping time of the impurity is increased and the thickness of the second electrode part 160 is increased in this manner, the characteristics of the doping process performed at a high temperature, the thermal expansion coefficient of the substrate 110 and the second electrode part 160 are shown. Due to the difference in the coefficient of thermal expansion of), the bowing phenomenon in which the center of the substrate 110 is convex as a whole occurs.

That is, the heat treatment process for forming the back electric field unit 170 of the substrate 110 is performed at a temperature of approximately 570 ℃. In addition, the thermal expansion coefficient of the substrate 110 made of a silicon material has a characteristic smaller than that of the second electrode unit 160 made of a conductive material.

In this case, after the heat treatment process is performed, the length of the second electrode unit 160 expanded and contracted by the heat treatment process is greater than the length of the substrate 110 expanded and contracted by the heat treatment process. In this case, since the shrinking length of the second electrode unit 160 becomes larger than that of the substrate 110, a bowing phenomenon occurs in which the entire shape of the solar cell is convex.

In consideration of such a problem, in order to form a thicker thickness of the second electrode unit 160 in order to form a thicker thickness of the rear electric field unit 170, and to perform a longer heat treatment time, the bowing as described above The bowing phenomenon may occur larger and eventually cause larger defects in the solar cell, which may lower the photoelectric conversion efficiency of the solar cell.

However, as in the present invention, when the first concave-convex portion having a size of 2 μm or less is included on the rear surface of the substrate 110 to form a larger surface area of the rear surface of the substrate 110, the second contacting substrate 110 is formed. The surface area of the electrode unit 160 also increases, and in addition, the amount of the metal material of the second electrode unit 160 diffused into the rear surface of the substrate 110 and doped also increases.

Therefore, even if the thickness of the second electrode unit 160 is made thicker or the heat treatment time for doping is not performed longer, the relatively thick rear electric field unit 170 may be formed.

Therefore, the present invention forms the first uneven portion having a size of 2 μm or less on the rear surface of the substrate 110, so that the second electrode portion 160 is formed on the rear surface of the substrate 110 even though the thickness of the second electrode portion 160 is relatively smaller. There is an effect that the thickness of the rear electric field unit 170 can be formed relatively larger.

Accordingly, the present invention can further increase the open voltage Voc of the solar cell while minimizing the above-mentioned bowing phenomenon, thereby further improving the photoelectric conversion efficiency of the solar cell.

For example, when there is no unevenness on the rear surface of the substrate 110 and the thickness of the second electrode portion 160 is 41.5 μm, the thickness of the rear electric field portion 170 formed with little boeing of the substrate 110 is Assuming that the thickness of the second electrode portion 160 is 41.5 μm, the first uneven portion P1 is further formed only on the rear surface of the substrate 110 to further increase the surface area of the rear surface of the substrate 110. When increased, the thickness of the backside electric field 170 formed with little boeing of the substrate 110 may be 6.3 μm to 7.3 μm, which is increased by 1 to 2 μm.

As such, when the first uneven portion P1 is formed on the rear surface of the substrate 110, when the thickness of the second electrode portion 160 is between 35 μm and 45 μm, the thickness of the rear electric field portion 170 is 5. Since the thickness may be formed to be between 9 μm and 9 μm, the thickness of the rear electric field part 170 may be further increased.

The emitter part 120 is formed on the front surface, which is the entrance surface of the substrate 110, and has a second conductivity type, for example, an n-type conductivity type, which is opposite to the conductivity type of the substrate 110. It is formed by doping the impurity to the substrate 110. Thus, the emitter portion 120 forms a p-n junction with the first conductivity type portion of the substrate 110.

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

Since the emitter portion 120 forms a p-n junction with the substrate 110, when the substrate 110 has an n-type conductivity type, the emitter portion 120 has a p-type conductivity type. In this case, electrons move toward the substrate 110 and holes move toward the emitter portion 120.

When the emitter part 120 has an n-type conductivity type, the emitter part 120 may be formed by doping the substrate 110 with impurities of a pentavalent element, and the emitter part 120 may have a p-type conductivity on the contrary. In the case of having a type, the emitter unit 120 may be formed by doping the substrate 110 with impurities of a trivalent element.

The emitter unit 120 is formed by diffusing and doping the second conductive type impurities from the front surface of the textured substrate 110 to the inside of the emitter unit 120. P2) can be formed.

More specifically, as shown in FIGS. 1 and 2, a plurality of second uneven portions P2 having relatively large sizes may be formed on the surface of the emitter portion 120 positioned on the front surface of the substrate 110. have. Here, the second uneven portion P2 formed on the surface of the emitter unit 120 will be described in detail with reference to the uneven portion formed on the surface of the rear electric field unit 170 in FIG. 3.

The anti-reflection unit 130 prevents light incident from the outside from being reflected back to the outside, and is formed on the front surface of the emitter unit 120. In more detail, the anti-reflection unit 130 may be formed on the front surface of the emitter portion 120 in which the first electrode portion 150 is not formed on the front surface of the substrate 110.

The anti-reflection unit 130 is made of a transparent material, and for example, a hydrogenated silicon nitride film (SiNx: H), a hydrogenated silicon oxide film (SiOx: H), or a hydrogenated silicon oxynitride film (SiOxNy: H). Or the like.

The anti-reflection unit 130 reduces the reflectivity of light incident on the solar cell 1 and increases the selectivity of a specific wavelength region, thereby increasing the efficiency of the solar cell 1.

In addition, through the injection of hydrogen (H) or the like when forming the anti-reflection portion 130, the anti-reflection portion 130 is a defect such as dangling bonds existing on the surface of and near the emitter portion 120. (defect) to a stable bond, and performs a passivation function (reduction) to reduce the dissipation of the charge moved to the surface of the emitter portion 120 by the defect. Therefore, the efficiency of the solar cell 1 is improved.

Since the anti-reflection portion 130 is formed by being deposited on the emitter portion 120, the surface of the anti-reflection portion 130 is the same as the second uneven portions P2 formed on the surface of the emitter portion 120. Unevenness of size may be formed.

In addition, in the present embodiment, the anti-reflection unit 130 is illustrated as an example of a single film structure, but may alternatively be formed as a multilayer film structure including a double film structure.

When the anti-reflection unit 130 has a multi-layered film structure, the anti-reflection unit 130 may be formed in contact with the emitter unit 120 directly to the upper portion of the emitter unit 120, and immediately above the lower anti-reflection film. It may be formed as an upper anti-reflection film formed in contact with.

Next, as illustrated in FIG. 1, the first electrode unit 150 includes a plurality of finger electrodes 151 and a plurality of front bus bars 152 formed in directions crossing each other, and the emitter unit 120. Is formed on the front upper portion of the emitter portion 120 is electrically connected.

However, unlike shown, the plurality of front busbars 152 may be omitted. However, hereinafter, as illustrated in FIG. 1, a case in which the plurality of front bus bars 152 are included in the first electrode unit 150 will be described as an example.

Here, the plurality of finger electrodes 151 and the plurality of front bus bars 152 are connected to each other, and the finger electrodes 151 and the front bus bars 152 are spaced apart from each other and extend side by side in a predetermined direction. The plurality of finger electrodes 151 and the plurality of front busbars 152 collect electric charges, for example, electrons moved toward the emitter unit 120.

In this case, the front busbar 152 is positioned on the same layer as the plurality of finger electrodes 151 and is electrically and physically connected to the corresponding finger electrodes 151 at the point where they cross each finger electrode 151.

Thus, as shown in FIG. 1, the plurality of finger electrodes 151 have a stripe shape extending in a direction crossing the front busbar 152, and the front busbar 152 has a finger electrode 151. Since it has a stripe shape extending in a direction intersecting with the first electrode part 150, the first electrode part 150 may be positioned in a lattice shape on the entire surface of the substrate 110.

Each of the front busbars 152 collects the charges collected by the plurality of finger electrodes 151 as well as the charges (eg, electrons) moving from the emitter unit 120, and moves them in a desired direction. The width of the 152 may be larger than the width of each finger electrode 151.

The front busbar 152 is connected to an external device to output the collected charges to the external device. The first electrode part 150 including the plurality of finger electrodes 151 and the front bus bar 152 is made of at least one conductive material such as silver (Ag).

In FIG. 1, the number of the finger electrodes 151 and the front busbars 152 positioned on the substrate 110 is only one example and may be changed in some cases.

The backside electric field unit 170 is a region in which impurities of the same conductivity type as the substrate 110 are doped 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 of the substrate 110 and the backside electric field 170, thereby preventing electrons from moving toward the backside electric field 170, which is the movement direction of the hole. The hole movement toward the rear electric field 170 becomes easier. Accordingly, the backside electric field 170 reduces the amount of charge lost due to the recombination of electrons and holes in the backside and the vicinity of the substrate 110 and accelerates the movement of the desired charge (for example, holes) so that the second electrode portion ( Increase the charge transfer to 160).

As described above, the rear electric field unit 170 is formed by diffusing and doping impurities of the first conductivity type from the rear surface of the substrate 110 to the inside, so that the rear surface of the rear electric field unit 170 is mentioned above. As described above, a plurality of relatively large second uneven portions P2 and a plurality of relatively small first uneven portions P1 positioned on the surface of the second uneven portions P2 are formed.

Here, the second uneven portion P2 formed on the rear surface of the rear electric field unit 170 and the second uneven portion P2 formed on the rear surface of the emitter unit 120 may be formed by the same etching process. , May have the same size range.

In addition, the first uneven portion P1 formed on the rear surface of the rear electric field unit 170 may be different from the second uneven portion P2 formed on the surface of the rear electric field unit 170 or the emitter unit 120. The size of the second uneven portion P2 may be smaller than that of the second uneven portion P2.

As described above, when the first uneven portion P1 and the second uneven portion P2 are formed on the rear surface of the rear electric field portion 170, the thickness of the second electrode portion 160 is between 35 μm and 45 μm. The thickness of the rear electric field unit 170 may be formed between 5 μm and 9 μm. The reason for setting the thickness of the rear electric field unit 170 in this way will be described with reference to FIGS. 4 and 5.

As such, the size of the second uneven part P2 formed on the surface of the emitter part 120 and the second uneven part P2 and the first uneven part P1 formed on the surface of the rear electric field part 170 are described. The size will be described later in detail with reference to FIG. 3.

The second electrode unit 160 is disposed on the rear surface of the semiconductor substrate 110, and as shown in FIG. 1, the second electrode unit 160 may include a rear electrode layer 161 and a rear bus bar 162. However, here, the rear busbar 162 may be omitted in some cases. The thickness of the second electrode unit 160, in particular, the thickness of the rear electrode layer 161 may be between 35 μm and 45 μm.

The rear electrode layer 161 is in contact with the rear electric field 170 located at the rear of the substrate 110, and may be substantially positioned on the entire rear of the substrate 110 except for a portion where the rear busbar 162 is located. have. Alternatively, the rear electrode layer 161 may not be located at the edge portion of the rear surface of the substrate 110. The rear electrode layer 161 contains a conductive material such as aluminum (Al).

The back electrode layer 161 collects charges, for example, holes, moving from the back field 170. In this case, since the rear electrode layer 161 is in contact with the rear electric field unit 170 having a higher impurity concentration than the substrate 110, the contact resistance between the rear electric field unit 170 and the rear electrode layer 161 is reduced, thereby reducing the substrate 110. ), The charge transfer efficiency to the rear electrode layer 161 is improved.

The plurality of rear busbars 162 are positioned on the rear surface of the substrate 110 in the region where the rear electrode layer 161 is not located and are connected to the adjacent rear electrode layer 161. In this case, the plurality of rear bus bars 162 and rear electrode layers 161 are positioned on the same layer on the rear surface of the substrate 110.

The plurality of rear busbars 162 collects charges transferred from the rear electrode layer 161, similar to the plurality of front busbars 152.

The plurality of rear busbars 162 are also connected to an external device, and the charges (eg, holes) collected by the plurality of rear busbars 162 are output to the external device.

The plurality of rear busbars 162 may be formed of a material having a better conductivity than the rear electrode layer 161. For example, unlike the rear electrode layer 161, at least one conductive material such as silver (Ag) may be used. It contains.

1 and 2, the rear bus bars 162 extend side by side in the same direction as the extension direction of the front bus bars 152 and are spaced apart from each other. In this case, the plurality of rear bus bars 162 may face the plurality of front bus bars 152 with respect to the substrate 110. In this example, the number of rear busbars 162 is the same as the number of front busbars 152.

Such a rear bus bar 162 may have, for example, a stripe shape parallel to the front bus bar 152.

The operation of the solar cell 1 according to this embodiment having such a structure is as follows.

When light is irradiated onto the solar cell 1 and incident on the emitter part 120 and the substrate 110, which are semiconductor parts, through the anti-reflection part 130, electrons and holes are generated in the semiconductor part by light energy. At this time, the reflection loss of the light incident on the substrate 110 by the anti-reflection unit 130 is reduced, so that the amount of light incident on the substrate 110 increases.

These electrons and holes are transferred to the emitter portion 120 by the pn junction of the substrate 110 and the emitter portion 120, for example, to the emitter portion 120. Move to each side.

Here, the electrons moved toward the emitter unit 120 are collected by the plurality of finger electrodes 151 and the plurality of front busbars 152, move along the plurality of front busbars 152, and toward the substrate 110. The moved holes are collected by the adjacent rear electrode layer 161 and the plurality of rear busbars 162 and move along the plurality of rear busbars 162. Therefore, when the front bus bar 152 of any one solar cell and the rear bus bar 162 of the adjacent solar cell are connected with a conductive wire, a current flows, which is used as power from the outside.

Meanwhile, the second uneven portion P2 and the first uneven portion P1 described above will be described in more detail as follows.

As shown in FIG. 3A, the plurality of second uneven portions P2 formed on the front surface of the emitter portion 120 may have impurities diffused on the front surface of the substrate 110 to form the emitter portion 120. , And has the same shape and size as the plurality of second uneven portions P2 formed on the front surface of the substrate 110 before the emitter portion 120 is formed on the front surface of the substrate 110. Since the plurality of second uneven parts P2 and the first uneven parts P1 formed on the rear surface of the rear electric field part 170 are also diffused on the rear surface of the substrate 110, the rear electric field part 170 is formed. The same shape and size as the plurality of first uneven parts P1 and the second uneven parts P2 formed on the rear surface of the substrate 110 before the rear electric field unit 170 is formed on the rear surface of the substrate 110 may be obtained. Have

In addition, since the second uneven parts P2 formed on the surfaces of the emitter part 120 and the rear electric field part 170 are formed by the same etching process, the second uneven parts P2 may have the same size as the first size.

In addition, as shown in FIG. 3B, the first uneven portion P1 formed on the surface of the second uneven portion P2 of the rear electric field unit 170 is formed on the surface of the rear electric field unit 170. The second uneven portion P2 may have a second size smaller than the first size.

More specifically, the height P2H of the second concave-convex portion P2 may be greater than the height P1H of the first concave-convex portion P1, and the distance between the protruding ends of the plurality of second concave-convex portions P2 ( P2D) may be greater than the distance P1D between the protruding ends of the plurality of first uneven parts P1.

As such, only the second uneven portion P2 is formed on the front surface of the emitter unit 120, and the second uneven portion P2 and the second uneven portion P2 are formed on the rear surface of the rear electric field unit 170. A relatively small first uneven portion P1 may be formed.

Here, as an example, the height P1H of the first uneven portion P1 may be 2 μm or less, and the height P2H of the second uneven portion P2 is larger than the first uneven portion P1. It can be made to be 5-15 micrometers or less within. In addition, the average height of the 1st uneven part P1 can be made into 300 nm-600 nm.

In addition, the interval P1D between the protruding ends of the first uneven parts P1 may be 2 μm or less, and the spacing P2D between the protruding ends of the second uneven parts P2 may include the first uneven part ( It can be set to 5-15 micrometers or less within the range larger than P1), and the average space | interval between the protruding ends of the 1st uneven | corrugated part P1 can also be set to be 300 nm-600 nm.

4 is a view for explaining the relationship between the thickness and the open voltage of the rear electric field, Figure 5 is a view for explaining the optimized thickness of the rear electric field according to the photoelectric conversion efficiency of the solar cell.

As shown in FIG. 4, as the thickness of the rear electric field unit 170 gradually increases, the open voltage of the solar cell also gradually increases.

As the thickness of the rear electric field unit 170 increases, the reason why the open voltage is increased is that as the thickness of the rear electric field unit 170 increases, the influence on the band off set voltage between the pn junctions increases. This is because the band offset voltage is increased.

As such, when the band offset voltage increases, the open voltage Voc of the solar cell increases. As the open voltage Voc of the solar cell increases, the photoelectric conversion efficiency of the solar cell also increases.

However, the thickness of the back field 170 and the photoelectric conversion efficiency of the solar cell are not always proportional.

Specifically, referring to FIG. 5, it can be seen that the photoelectric conversion efficiency of the solar cell does not continuously increase even if the thickness of the rear electric field unit 170 continuously increases.

More specifically, as the thickness of the rear electric field unit 170 increases from 1 μm to 7 μm, the efficiency of the solar cell increases nonlinearly, but the thickness of the rear electric field unit 170 is greater than 7 μm. When the thickness of the rear electric field unit 170 is increased to 10 μm, the efficiency of the solar cell may be further reduced.

As such, even if the thickness of the rear electric field unit 170 continuously increases, the efficiency of the solar cell does not continuously increase in proportion, but rather decreases after a certain thickness (7 μm). Because.

That is, impurities included in the rear electric field unit 170 act as defects in the solar cell, and when the amount of impurities included in the rear electric field unit 170 exceeds a certain range, the open voltage Voc increases. This is because the magnitude of decreasing the short-circuit current Isc increases more than the magnitude.

Accordingly, in consideration of both the synergistic effect of the open voltage Voc and the reduction effect of the short circuit current Isc according to the thickness of the rear electric field unit 170, the solar cell according to the present invention increases the thickness of the rear electric field unit 170. It can be set between 5 µm and 9 µm.

In addition, setting the thickness of the rear electric field unit 170 to 5 μm to 9 μm is to ensure efficiency stability of the solar cell. More specifically, it is very difficult to accurately set the thickness of the rear electric field unit 170 in μm. That is, as described above, the thickness of the rear electric field unit 170 may vary depending on the thickness of the second electrode and the execution time of the heat treatment process for diffusion, so that the amount diffused from the rear surface of the substrate 110 to the inside may vary. .

Therefore, except for a thickness range (less than 5 μm) in which the efficiency of the solar cell varies greatly according to the thickness of the rear electric field unit 170, the efficiency of the solar cell is relatively slow even if the thickness of the rear electric field unit 170 changes. The thickness of the rear electric field unit 170 is formed between 5 μm and 9 μm, which is varied so that the efficiency of the plurality of solar cells may be set more uniformly even when a plurality of solar cells are produced.

However, the thickness range of the rear electric field unit 170 is not necessarily limited to between 5 μm and 9 μm.

Hereinafter, an example of a method of manufacturing the solar cell according to the present invention described above will be described.

6A to 6G are diagrams for explaining an example of the solar cell manufacturing method according to the present invention.

First, as shown in FIG. 6A, an ingot, which is single crystal silicon doped with impurities of a first conductivity type, is cut to prepare a substrate 110 for the solar cell 1, and the front and rear surfaces of the substrate 110 are prepared. The damage layer is removed by saw damage etching to remove the generated damage layer.

Thereafter, as shown in FIG. 6B, anisotropic etching is performed to texture the front and rear surfaces of the substrate 110. At this time, a relatively large second uneven portion P2 is formed on the front and rear surfaces of the substrate 110 by anisotropic etching.

Here, the etching solution used for the anisotropic etching may be an alkaline solution. Such an alkaline solution may include potassium hydroxide (KOH) or sodium hydroxide (NaOH), and may further include IPA (Iso Propyl Alcohol) and D-I Water (De Ionized Water) containing no impurities.

On the other hand, in the solar cell manufacturing method according to the present invention has been described as an example of performing anisotropic etching to texturize the substrate 110 after the saw damage etching, this step may be omitted. .

For example, when the substrate 110 is polycrystalline, as shown in FIG. 6A, only the damage damage etching may be performed, and anisotropic etching may be omitted. However, since FIGS. 6A to 6G illustrate an example in which the substrate 110 is a single crystal silicon substrate, an example of performing anisotropic etching will be described below.

Thereafter, as shown in FIG. 6C, reactive ion etching (RIE) is performed on the rear surface of the substrate 110.

As described above, a process of performing reactive ion etching is performed. First, the substrate 110 is placed in a process chamber having a pressure of about 0.1 to 0.5 mTorr, and then a mixture of SF6 and O2 (SF6 / O2) or SF6 and An etching gas, which is a mixed gas of O 2 and Cl 2 (SF 6 / Cl 2 / O 2), is injected into the process chamber.

Then, when power of the corresponding size is applied to two electrodes (not shown) provided between the substrates 110, plasma based on the source gas is generated in the space between the two electrodes, thereby etching operation by the generated plasma, That is, the dry etching operation is performed. At this time, the magnitude of the power applied to the electrode may be about 3000W / m2 ~ 6000W / m2.

By the reactive ion etching, the first uneven portion P1 having a smaller size than the second uneven portion P2 is formed on the inclined surface of the second uneven portion P2 formed on the rear surface of the substrate 110.

As such, the first uneven portion P1 formed on the rear surface of the substrate 110 increases the surface area of the rear surface of the substrate 110 to increase the thickness of the rear electric field portion 170 formed on the rear surface of the substrate 110. To help.

Next, as shown in FIG. 6D, the present invention diffuses impurities of the second conductivity type opposite to the first conductivity type into the front surface of the substrate 110 on which the second uneven portion P2 is formed to form the emitter portion 120. Let's do it.

As a result, a plurality of second uneven portions P2 are formed on the surface of the emitter portion 120.

Here, the detailed description of the second uneven part P2 formed on the surface of the emitter part 120 is the same as described above with reference to FIGS. 1 to 3, and thus will be omitted.

Then, as shown in Figure 6e, the present invention can form the anti-reflection portion 130 on the upper surface of the emitter portion 120. The anti-reflection unit 130 may be formed using a chemical vapor deposition (CVD) method, such as plasma enhanced chemical vapor deposition (PECVD), and has an example of a single film structure. Alternatively, however, the multilayer film structure may have a double layer structure.

Thereafter, as shown in FIG. 6F, the first paste 150 ′ including the finger electrode pattern 151 ′ and the front busbar pattern 152 ′ is formed on the anti-reflection portion 130, and The second paste 160 ′ including the rear electrode layer pattern 161 ′ and the rear bus bar pattern 162 ′ is formed on the rear surface of the substrate 110.

In this case, the first electrode paste 150 ′ may include silver (Ag), for example, and the rear electrode layer pattern 161 ′ of the second electrode paste 160 ′ may include aluminum (Al), and a rear bus bar. The pattern 162 ′ may include silver (Ag).

Next, as illustrated in FIG. 6G, the first paste 150 ′ and the second paste 160 ′ may be simultaneously heat-treated to form the first electrode 150 and the second electrode 160.

As such, by simultaneously heat-treating the first paste 150 ′ and the second paste 160 ′, the heat treatment process may be simplified, and the amount of damage that may be caused to the substrate 110 by the heat treatment process may be minimized. have.

In detail, when the first paste 150 ′ is heat-treated, the first paste 150 ′ positioned above the anti-reflective unit 130 penetrates the anti-reflective unit 130 and is electrically connected to the emitter unit 120. It is formed of a first electrode portion 150 to be connected.

In addition, when heat treating the second paste 160 ′, some of aluminum (Al) contained in the back reflective layer pattern 161 ′ of the second paste 160 ′ diffuses from the rear surface of the substrate 110 to the inside. And doped to form the rear electric field unit 170 at the same time.

Such a rear electric field unit 170 is relatively compared to the case where only the second uneven portion P2 is formed due to the first uneven portion P1 and the second uneven portion P2 formed on the rear surface of the substrate 110. It may be formed on the back of the substrate 110 to a greater thickness.

In addition, the first uneven portion P1 and the second uneven portion P2 formed on the rear surface of the substrate 110 may have a relatively smaller amount of the second paste 160 'and the second paste 160'. In spite of the heat treatment time, by helping to form the backside electric field 170 having a sufficient thickness, it is possible to reduce the manufacturing cost of the solar cell and to further shorten the process time.

In addition, the substrate 110 having a rear surface having a larger surface area due to the first uneven portion P1 and the second uneven portion P2 may have a relatively small amount of the second paste 160 ′. By forming the rear electric field 170, the bowing of the substrate 110 due to the difference in the coefficient of thermal expansion between the substrate 110 and the second paste 160 ′ may be minimized, and the solar cell The efficiency can be further improved.

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

Claims (13)

A substrate doped with impurities of a first conductivity type;
An emitter unit disposed on a front surface of the substrate and doped with impurities of a second conductivity type opposite to the first conductivity type to form a pn junction with the substrate;
A rear electric field unit positioned on a rear surface of the substrate and doped with a higher concentration of impurities of the first conductivity type than the substrate;
A first electrode part electrically connected to the emitter part; And
And a second electrode part electrically connected to the rear electric field part.
A rear surface of the rear electric field portion has a first uneven portion having a size of 2 μm or less; And
A second uneven portion having a larger size than the first uneven portion,
The first uneven portion is a solar cell formed on the surface of the second uneven portion. delete The method according to claim 1,
The protruding height of the first uneven portion is smaller than the protruding height of the second uneven portion. The method according to claim 1,
The protruding height of the first uneven portion is 2 μm or less, and the protruding height of the second uneven portion is 5 to 15 μm. The method according to claim 1,
The thickness of the second electrode portion is a solar cell between 35㎛ 45㎛. The method according to claim 1,
The thickness of the rear electric field is between 5㎛ ~ 9㎛ solar cell. Forming a first uneven portion on the back surface of the substrate having the first conductivity type;
Forming an emitter portion including impurities of a second conductivity type opposite to the first conductivity type on an entire surface of the substrate; And
And diffusing the same impurity as the first conductivity type into the back surface of the substrate on which the first uneven portion is formed at a higher concentration than the substrate, thereby forming a rear electric field portion.
Before forming the first uneven portion,
A solar cell manufacturing method for forming a second uneven portion larger than the first uneven portion on the back surface of the substrate. The method of claim 7, wherein
The first uneven portion is a solar cell manufacturing method formed by reactive ion etching (RIE). The method of claim 7, wherein
The second uneven portion is formed by performing an anisotropic etching on the back surface of the substrate. 10. The method of claim 9,
The anisotropic etching is a solar cell manufacturing method performed by alkaline solution (alkaline solution). The method of claim 10,
The alkaline solution is a solar cell manufacturing method comprising potassium hydroxide (KOH) or sodium hydroxide (NaOH). The method of claim 7, wherein
Applying a first paste for forming a first electrode portion on the entire surface of the substrate; And
Applying a second paste for forming a second electrode portion on a rear surface of the substrate; The method of claim 12,
And forming the rear electric field at the same time when the first paste and the second paste are heat-treated to form the first electrode portion and the second electrode portion.

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