KR101282929B1 - Solar cell and method of preparing the same - Google Patents

Abstract

The present invention relates to a solar cell and a method of manufacturing the same. The solar cell of the present invention includes a first conductive semiconductor substrate, a second conductive semiconductor layer formed on the first conductive semiconductor substrate and having a conductivity opposite to that of the first conductive semiconductor substrate, and the first conductive semiconductor. A pn structure formed of a pn junction formed at an interface between a substrate and a second conductive semiconductor layer. An antireflection film formed on the second conductive semiconductor layer. The antireflection film is formed on the antireflection film and penetrates the antireflection film to form a second conductivity. It includes a front electrode connected to the type semiconductor layer and a predetermined intaglio pattern on the surface and comprises a back electrode formed on the first conductive semiconductor substrate. The solar cell of the present invention not only reduces the occurrence of the cell bowing phenomenon but also controls the degree and direction of the cell bowing phenomenon, thereby exhibiting excellent performance because of a low risk of breakage and a high absorption rate against sunlight.

Solar cell, photovoltaic effect, semiconductor, side spread phenomenon, cell bowing, non-printing line

Description

Solar cell and its manufacturing method {Solar cell and method of preparing the same}

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to.

1 is a schematic diagram showing the basic structure of a solar cell.

2 is a view schematically showing a solar cell according to an embodiment of the present invention.

3 to 5 are diagrams showing examples of the intaglio pattern of the rear electrode of the solar cell of the present invention.

6 is a diagram schematically showing a stacking state by a cassette method of a solar cell according to the prior art (left) and the present invention (right).

7 is a view schematically showing a stacking state by a magazine method of the solar cell according to the prior art (left) and the present invention (right).

8A to 8C are diagrams for explaining the principle that the side spread phenomenon is used in the present invention.

9A to 9C are views for explaining a method of forming a back electrode of the present invention.

The present invention relates to a solar cell and a method for manufacturing the solar cell, and more particularly, to control the direction and extent of the cell bowing phenomenon caused by the difference in thermal expansion coefficient between the solar cell and the back electrode of the solar cell The present invention relates to a solar cell and a method for manufacturing the solar cell, which can prevent or reduce bowing.

With the recent depletion of existing energy resources such as oil and coal, interest in alternative energy to replace them is increasing. Among them, solar cells are particularly attracting attention because they are rich in energy resources and have no problems with environmental pollution. Solar cells include solar cells that generate steam for rotating turbines using solar heat, and solar cells that convert photons into electrical energy using the properties of semiconductors. Refers to photovoltaic cells (hereinafter referred to as solar cells).

Referring to FIG. 1 showing the basic structure of a solar cell, a solar cell has a junction structure of a p-type semiconductor 101 and an n-type semiconductor 102 like a diode, and when light is incident on the solar cell, Interaction with the materials that make up the semiconductor causes electrons with negative charge and electrons to escape, creating holes with positive charge, and as they move, current flows. This is called a photovoltaic effect. Among the p-type 101 and n-type semiconductors 102 constituting the solar cell, electrons move toward the n-type semiconductor 102 and holes are p-type semiconductors. Pulled toward 101 and moved to the electrodes 103 and 104 bonded to the n-type semiconductor 101 and the p-type semiconductor 102, respectively, and when the electrodes 103 and 104 are connected by wires, electricity flows. Power can be obtained.

The output characteristics of the solar cell are generally evaluated by measuring the output current voltage curve using a solar simulator, and the point where the product Ip X Vp of the output current Ip and the output voltage Vp becomes maximum on the curve is called maximum output Pm, The value obtained by dividing Pm by the total light energy incident on the solar cell (SXI: S is the device area and I is the intensity of light irradiated to the solar cell) is defined as the conversion efficiency η. To increase the conversion efficiency η, increase the short-circuit current Is (output current when V = 0 on the current voltage curve) or open voltage Voc (output voltage when I = 0 on the current voltage curve) or the square of the output current voltage curve. You should increase the fill factor (FF), which is close to.

In such a solar cell, the back electrode is typically formed by printing a paste and heat-treating the entire surface opposite to the surface on which the front electrode is formed with a silicon substrate therebetween. However, the thermal expansion coefficient of aluminum, which is generally used to form the back electrode, is greater than that of the silicon substrate, so that a cell bowing phenomenon occurs in which the silicon substrate is bent by heat treatment for forming the back electrode. The cell bowing phenomenon causes a great difficulty in stacking after fabrication of the solar cell, increases the risk of product breakdown, and lowers the absorption rate of solar light, thereby degrading the performance of the solar cell. Accordingly, efforts to prevent or reduce such cell bowing have been steadily made in the related field, and the present invention has been made under such a technical background.

The present invention has been made to solve the above-mentioned problems of the prior art, and the technical problem to be achieved by the present invention is the direction of the cell bowing phenomenon caused by the difference in the coefficient of thermal expansion between the back electrode of the solar cell and the semiconductor substrate and The present invention is to provide a solar cell and a method for manufacturing the same, which control the degree and further prevent or reduce cell bowing, thereby reducing the risk of solar cell breakdown and improving performance. There is a purpose.

SUMMARY OF THE INVENTION In order to achieve the technical problem to be achieved by the present invention, the present invention is a first conductivity type semiconductor substrate, a second conductivity type formed on the first conductivity type semiconductor substrate and having a conductivity type opposite to that of the first conductivity type semiconductor substrate. A pn structure formed of a semiconductor layer and a pn junction formed at an interface between the first conductivity type semiconductor substrate and the second conductivity type semiconductor layer; an antireflection film formed on the second conductivity type semiconductor layer; A solar cell comprising a front electrode connected to the second conductive semiconductor layer through the anti-reflection film and a back electrode formed on the first conductive semiconductor substrate and including a predetermined intaglio pattern on the surface thereof. to provide.

In the solar cell, the first conductive semiconductor substrate is a p-type silicon substrate, and the second conductive semiconductor layer is an n-type emitter layer, and an interface between the first conductive semiconductor substrate and the back electrode. It is preferable that a p + layer be formed in the. The surface of the back electrode is preferably formed in a stripe, lattice or concentric intaglio pattern. The anti-reflection film may be typically formed of silicon nitride.

The present invention also provides a method for forming a back electrode of a solar cell using screen printing, the method comprising: printing a back electrode forming paste so as to have a predetermined intaglio pattern on the semiconductor substrate, and heat treating the semiconductor substrate on which the paste is printed. It provides a method for forming a back electrode of a solar cell.

The screen mesh used for printing the paste includes a support and a non-printing line formed on the support so that the paste does not pass through the support, wherein the distance between the non-printing lines corresponds to the intaglio portion of the back electrode. Preferably, the portion is formed smaller than the portion corresponding to the embossed portion of the back electrode. Preferably, the width of the non-printed line of the screen mesh is several to 80 μm, and the interval between the non-printed lines at the portion corresponding to the negative portion of the engraved pattern of the screen mesh is several to 80 μm, Preferably, the interval between the non-printed lines in the portion corresponding to the embossed portion of the engraved pattern of the screen mesh is 80 μm or more. The intaglio pattern may be typically formed in a stripe shape, a lattice shape or a concentric shape, and the paste is preferably made of aluminum. The viscosity of the paste is 50-1200 poise, preferably 200-700 poise.

The present invention also provides a method for manufacturing a solar cell including the back electrode forming method and a solar cell manufactured using the manufacturing method.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings to assist in understanding the present invention.

2 is a schematic cross-sectional view of a solar cell according to an embodiment of the present invention. As shown in FIG. 2, the solar cell of the present invention includes a p-n structure, an antireflection film 205, a front electrode 203, and a rear electrode 204.

The pn structure is formed on the first conductive semiconductor substrate 201 and the second conductive semiconductor substrate 201 and has a second conductivity-type semiconductor layer having a conductivity opposite to that of the first conductive semiconductor substrate 201 ( 202 and a pn junction formed at an interface between the first conductivity type semiconductor substrate 201 and the second conductivity type semiconductor layer 202, and receive light to generate a current by a photovoltaic effect. Typically, the first conductivity-type semiconductor substrate 201 is a p-type silicon substrate doped with Group III elements such as B, Ga, In, and the like, and the second conductivity-type semiconductor layer 202 is For example, an n-type emitter layer doped with Group 5 elements such as P, As, and Sb, and the p-type silicon substrate and the n-type emitter layer may contact each other to form a pn junction. However, the p-n structure is not limited thereto.

The anti-reflection film 205 may be formed on the p-n structure of the second conductivity-type semiconductor layer 202 to improve the photoelectric conversion efficiency of the solar cell by reducing the reflectance to sunlight. The anti-reflection film may be typically formed of silicon nitride, but is not limited thereto. Various methods may be used to form the antireflection film, including plasma chemical vapor deposition (PECVD), chemical vapor deposition (CVD), or sputtering. In addition, a passivation layer may be separately formed between the second conductivity-type semiconductor layer 202 and the anti-reflection film 205.

The front electrode 203 is formed on the anti-reflection film 205 and is connected to the second conductive semiconductor layer through the anti-reflection film. A silver electrode is typically used as the front electrode 203 because the silver electrode has excellent electrical conductivity. If the area of the front electrode is large, the absorption rate of sunlight decreases, and if the area of the front electrode is narrow, the resistance between the second conductive semiconductor layer is large. Therefore, the pattern of the front electrode can be formed in consideration of these.

The back electrode 204 is formed on the first conductive semiconductor substrate, and a predetermined intaglio pattern is formed on the surface of the back electrode 204 to generate a step between the indentation part and the intaglio part. The shape of the pattern is not particularly limited and may be formed in various shapes, including the stripe of FIG. 3, the lattice of FIG. 4, and the concentric circles of FIG. 5. This intaglio pattern can alleviate cell bowing due to a difference in thermal expansion coefficient, and can appropriately control the degree and direction of cell bowing of a solar cell produced in large quantities. Through this, it is possible to reduce the risk of breakage of the solar cell, to facilitate the stacking (stacking) of the solar cell, it is possible to improve the absorption of sunlight.

6 is a diagram schematically showing a stacking state by a cassette method of a solar cell according to the prior art (left) and the present invention (right). As shown in FIG. 6, according to the related art, since cell bowing is non-uniform, the gap between wafers is different when loading / unloading to increase the risk of breakage, and during wafer chucking using a vacuum. Since wafer bowing is different, the possibility of a chucking defect arises. The wafer chucking means to hold the wafer by a vacuum adsorption method in order to proceed with the subsequent process for the solar cell wafer.

7 is a view schematically showing a stacking state by a magazine method of the solar cell according to the prior art (left) and the present invention (right). As shown in FIG. 7, according to the present invention, since the bowing of the wafer is constant, stacking can be made more densely, and stress on the lower wafer is less stressed.

An aluminum electrode is typically used as the back electrode 204 because the aluminum electrode not only has excellent conductivity but also has a good affinity with silicon, so that the electrode is well bonded. In addition, since the aluminum electrode is a trivalent element, the p + layer, that is, the back surface field (BSF), is formed at the interface with the silicon substrate so that carriers can be collected without disappearing from the surface, thereby increasing efficiency.

The present invention provides a method for forming a back electrode of a solar cell and a method of manufacturing a solar cell including the same, which can form a back electrode having a negative pattern on a surface as described above in a simple process and at low cost.

The method of forming a back electrode of the present invention includes printing a back electrode forming paste to have a predetermined negative pattern on the semiconductor substrate by using screen printing, and heat treating the paste-printed semiconductor substrate.

The present invention may use the side spread phenomenon of the paste in order to more easily form the intaglio pattern in the paste printing step. 8A to 8C are diagrams for explaining the principle that the side spread phenomenon is used in the present invention. The principle in which the side spread phenomenon is applied to the present invention will be described using the above drawings.

First, a screen mesh with a non-printing line 403 is placed on a mesh support 402 on the semiconductor substrate 401 (FIG. 8A), and the paste 405 is moved while the screen printer 404 moves in the direction of the arrow. Is pushed between the unprinted lines 403 through the support 402 of the screen mesh (FIG. 8B). Then, when the screen meshes 402 and 403 are removed from the semiconductor substrate 401, they spread around by the side spread phenomenon of the paste 405. As the width of the printed paste 405 is wider, the side spread phenomenon occurs. The height reduction by is small (FIG. 8C). Therefore, the larger the width of the printed paste 405 is, the larger the height becomes.

9A to 9C are views for explaining a method of forming a back electrode of the present invention. With reference to the drawings looks at in detail with respect to the method of forming a back electrode of the present invention.

When the intaglio pattern of the back electrode is determined, a small amount of paste 405 should be applied to the region where the intaglio portion of the back electrode is to be formed, and a larger amount of paste 405 in the region where the indentation portion of the back electrode is to be formed. Should be applied. Thus, the screen mesh is prepared such that the spacing Lb, Lc between the non-printed lines 403 is made smaller than in the portion corresponding to the indentation of the back electrode in the portion corresponding to the intaglio portion of the back electrode (Fig. 9a). When the screen meshes 402 and 403 thus prepared are placed on the semiconductor substrate 401 and the screen printer 404 is moved, the paste 405 is filled with empty spaces between the non-printed lines 403 (FIG. 9B). When the screen meshes 402 and 403 are removed, the paste is printed thinner (9c) in the region where the spacing between the non-printed lines is narrow compared to the region where the spacing between the non-printed lines is wide.

In the method of forming the back electrode, the width La of the non-printing line 403 of the screen mesh is not particularly limited, and considering the viscosity of the electrode forming paste 405 that is commonly used, it is several to 80 μm. desirable. In addition, the interval between the non-printed lines 403 is a gap between the non-printed lines 403 at portions corresponding to the embossed portions of the back electrode, considering the viscosity of the conventional paste 405 and the thickness of the electrode. It is preferable that Lc) is 80 micrometers or more, and the space | interval Lb between the non-printed lines 403 in the part corresponding to the intaglio part of the said back electrode is preferably several to 80 micrometers.

The intaglio pattern may be typically formed in a stripe shape, a lattice shape, or a concentric shape, but is not limited thereto. Moreover, it is preferable that the said paste contains aluminum. The viscosity of the paste is 50 to 1500 poise, preferably 200 to 700 poise in consideration of the degree of side spreading and the like.

The solar cell manufacturing method of the present invention can manufacture a solar cell by employing well-known techniques in addition to the back electrode forming method.

The terms or words used in this specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors can appropriately define the concept of terms in order to best describe their invention. Based on the principle, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Therefore, the exemplary embodiments described herein are only exemplary embodiments of the present invention and do not represent all of the technical ideas of the present invention, and various equivalents and modifications that may substitute them at the time of the present application may be used. It should be understood that there may be.

The solar cell of the present invention not only reduces the occurrence of the cell bowing phenomenon but also controls the degree and direction of the cell bowing phenomenon, thereby exhibiting excellent performance because of a low risk of breakage and a high absorption rate against sunlight. In addition, according to the method for forming the back electrode and the solar cell of the solar cell of the present invention, the solar cell as described above can be manufactured in a simple process and low cost.

Claims (16)

A first conductivity type semiconductor substrate, a second conductivity type semiconductor layer formed on the first conductivity type semiconductor substrate and having a conductivity opposite to the first conductivity type semiconductor substrate, and the first conductivity type semiconductor substrate and the second conductivity type. Pn structure consisting of pn junctions formed at interfaces between semiconductor layers An antireflection film formed on the second conductive semiconductor layer A front electrode formed on the antireflection film and penetrating the antireflection film to be connected to a second conductive semiconductor layer; A solar cell comprising a back electrode formed on the first conductive semiconductor substrate and including a predetermined intaglio pattern on a surface thereof. The method of claim 1, The first conductive semiconductor substrate is a p-type silicon substrate, the second conductive semiconductor layer is an n-type emitter layer, characterized in that the solar cell. The method of claim 1, And a p + layer is formed at an interface between the first conductive semiconductor substrate and the back electrode. The method of claim 1, The surface of the back electrode, the stripe, lattice or concentric intaglio pattern is formed solar cell, characterized in that formed. The method of claim 1, The anti-reflection film is a solar cell, characterized in that formed of silicon nitride. In the method of forming the back electrode of the solar cell using screen printing, Printing a paste for forming a back electrode on the semiconductor substrate to have a predetermined intaglio pattern; and The method of forming a back electrode of a solar cell comprising the step of heat-treating the semiconductor substrate printed with the paste. The method of claim 6, The screen mesh used for printing the paste includes a support and a non-printing line formed on the support so that the paste does not pass through the support, wherein the distance between the non-printing lines corresponds to the intaglio portion of the back electrode. The rear electrode forming method of the solar cell, characterized in that formed in the portion smaller than the portion corresponding to the embossed portion of the back electrode. The method of claim 7, wherein The width of the non-printed line of the screen mesh is a method of forming a back electrode of the solar cell, characterized in that a few ~ 80㎛. The method of claim 7, wherein The distance between the non-printed line in the portion corresponding to the negative portion of the back electrode of the screen mesh is a method of forming a back electrode of the solar cell, characterized in that a few ~ 80㎛. The method of claim 7, wherein The gap between the non-printed line in the portion corresponding to the embossed portion of the back electrode of the screen mesh is a method of forming a back electrode of the solar cell, characterized in that more than 80㎛. The method of claim 6, The intaglio pattern is a stripe, lattice or concentric intaglio pattern of the solar cell, characterized in that the intaglio pattern. The method of claim 6, The paste is a method of forming a back electrode of a solar cell, characterized in that containing aluminum. The method of claim 6, The paste has a viscosity of 50 ~ 1500 poise, the method of forming a back electrode of a solar cell. The method of claim 6, The paste has a viscosity of 200 ~ 700 poise solar cell back electrode forming method, characterized in that. The method of manufacturing a solar cell comprising the method of forming a back electrode according to any one of claims 6 to 14. A solar cell manufactured using the manufacturing method according to claim 15.

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