WO2011138998A1 - Composition for manufacturing a back contact for a crystalline solar cell - Google Patents

Abstract

The present invention relates to a composition for manufacturing a back contact for a crystalline solar cell. The back contact material used for manufacturing a crystalline solar cell, a front contact and back contact of which are formed on the front side and rear side of a wafer, respectively, comprises a mixture composition consisting of an acrylate- or cellulose-based resin, aluminum powder, an inorganic binder, and an additive for increasing adhesion to a wafer, wherein the aluminum powder is a powder mixture containing aluminum powder, the size of which is 30-100 nm, and aluminum powder, the size of which is 2-10 µm. The composition of the present invention uses said types of aluminum powder, the sizes of which are smaller than those disclosed in prior art, thereby reducing Rs-contact resistance and thus enabling a solar cell to have excellent photoelectric conversion efficiency.

Description

Composition for preparing crystalline solar cell back electrode

The present invention relates to a composition for preparing a crystalline solar cell back electrode, and in particular, to use an aluminum powder of a smaller size (size) than in the prior art, more specifically, it is possible to lower the series resistance (Rs_contact resistance) value, accordingly The present invention relates to a back electrode material for manufacturing a high efficiency solar cell capable of having a remarkably excellent photoelectric conversion efficiency (Efficiency).

In general, a crystalline solar cell is mainly a silicon material is used as a semiconductor device that converts solar energy directly into electricity, as shown in Figure 1, the silicon wafer 10 and the silicon wafer (basically forming a pn junction structure) ( 10 is formed on the top surface of the anti-reflection film 20 and the silicon wafer 10 and the printed on the upper surface and the lower surface of the silicon wafer 10 so as to be able to absorb light well inside the solar cell 10 It consists of a front electrode 30 and a rear electrode 40 for drawing the electricity generated to the outside.

Silver (Ag) is used as the main electrode material as the front electrode 20 and aluminum (Al) is used as the main electrode material as the back electrode 40.

In addition, instead of forming the anti-reflection film 20 on the silicon wafer 10, the surface may be roughened to reduce the reflectance of incident sunlight.

In the solar cell having the above configuration, as shown in FIG. 2, when sunlight is incident and absorbed into the silicon wafer, the absorbed light generates positive (+) (−) charges inside the wafer and p in the wafer. The electrons (-) and holes (+) of the charge generated by the potential difference created at the pn junction of the silicon and the n-type silicon are separated, and the electrons move toward the n-type silicon and the holes move toward the p-type silicon. Collected by the electrode and the rear electrode is the rear electrode becomes the anode and the front electrode becomes the cathode to be able to supply electricity.

By the way, the conventional rear electrode used in the crystalline solar cell as described above is formed by a process of printing and baking and modularizing the aluminum paste, which is the back electrode material on the silicon wafer, conventionally fired for manufacturing the crystalline solar cell Due to the stress caused by the difference in thermal expansion coefficient between the wafer and the back electrode during the sintering process, there was a problem that bowing phenomenon occurred due to the bending or bending of the wafer after the firing process. In addition to this, it is difficult to apply a thin film silicon wafer, which causes a cost increase of the wafer in manufacturing a solar cell.

On the other hand, the inventors of the Republic of Korea Patent No. 10-0801168 (announced 2008.02.05) as a high-efficiency solar cell back electrode material, the acrylate (acrylate) or cellulose (cellulose) resin 0.5 to 20 parts by weight A mixed composition consisting of 40 to 90 parts by weight of powder, 0.5 to 10 parts by weight of inorganic binder, and 0.1 to 10 parts by weight of an additive for increasing adhesion to the wafer was registered.

However, there is a problem in that the back electrode material for manufacturing a high efficiency solar cell made of the mixed composition has a high series resistance (Rs_contact resistance) value and thus insufficient photoelectric conversion efficiency (Efficiency).

In addition, in order to increase the efficiency of the crystalline solar cell, the bowing phenomenon should be further reduced without degrading the photoelectric conversion efficiency. However, the back electrode material can no longer reduce the bowing phenomenon.

An object of the present invention for solving the above problems is to provide a composition for preparing a crystalline solar cell back electrode that can lower the series resistance (Rs_contact resistance) value, thereby having a significantly superior photoelectric conversion efficiency (Efficiency). .

In addition, in order to increase the efficiency of the solar cell in the trend that the thickness of the wafer is gradually thinner, to provide a high efficiency solar cell back electrode material that can further reduce the bowing (bowing) phenomenon without deterioration of the photoelectric conversion efficiency.

The present invention for achieving the above object is a composition for manufacturing a back electrode used to manufacture a crystalline solar cell in which the front electrode and the back electrode is formed on the front, back of the wafer, acrylate (acrylate) or cellulose (cellulose) ) Is composed of a mixture of a resin, an aluminum powder, an inorganic binder, and an additive for increasing adhesion to the wafer. The aluminum powder is composed of an aluminum powder having a size of 30 to 100 nanometers, It is a composition for preparing a crystalline solar cell back electrode, characterized in that the aluminum powder of 2 ~ 10 micron size is mixed.

Here, the aluminum powder is preferably mixed with 0.01 to 7.0 parts by weight of aluminum powder of 30 to 100 nanometers and 39.9 to 85.0 parts by weight of aluminum powder of 2 to 10 microns.

In addition, the mixed composition may further comprise a fumed silica (fumed silica), the fumed silica (fumed silica) is 0.01 to 0.01 to 20 parts by weight based on acrylate (acrylate) or cellulose (cellulose) resin It can be included in 10 parts by weight.

Other features of the invention are described in the detailed description and drawings of the invention which follow.

The present invention described above is a composition for preparing a crystalline solar cell back electrode comprising a mixture composition of an acrylate-based or cellulose-based resin, an aluminum powder, an inorganic binder, and an additive for increasing adhesion to a wafer. By using an aluminum powder having a smaller size than the related art, the series resistance (Rs_contact resistance) value can be lowered, thereby making it possible to have a remarkably excellent photoelectric conversion efficiency.

In addition, in order to increase the efficiency of the crystalline solar cell in the trend that the thickness of the wafer gradually becomes thin, the bowing phenomenon should be further reduced without decreasing the photoelectric conversion efficiency, the present invention further comprises a porous silica (fumed silica) By using a mixed composition, there is an effect that can reduce the bowing phenomenon remarkably superior to the conventional.

1 is a cross-sectional view showing the structure of a typical crystalline solar cell.

2 is a schematic diagram for explaining the principle of a typical crystalline solar cell,

3 is a block flow diagram illustrating an example of a manufacturing process of the composition for preparing a crystalline solar cell back electrode according to the present invention;

Figure 4 is a graph showing an example of the series resistance value according to the content of aluminum nano powder in the back electrode material prepared according to the present invention and the prior art,

5 is a graph showing an example of the series resistance value according to the particle size of the aluminum powder in the back electrode material according to the present invention,

6 is a graph showing the bending characteristics according to the printing thickness of the electrode material in each of the back electrode material containing porous silica and the back electrode material not containing porous silica according to the prior art,

Figure 7 is a schematic diagram showing the measurement of the light conversion efficiency of the crystalline solar cell using the back electrode material of the present invention.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail.

3 is a block flow diagram for explaining an example of the manufacturing process of the composition for producing a crystalline solar cell back electrode according to the present invention.

As shown here, the composition for preparing a crystalline solar cell rear electrode according to the present invention comprises a first step (S1) of washing the raw material input container, and the resin, inorganic binder and additives in the raw material input container of the first process. A second step (S2) of measuring and injecting a base material, a third step (S3) of mixing the base material introduced into the raw material input container through a mixing machine, and a blending material having undergone the third process A fourth step S4 of pulverizing, mixing and extruding the blended raw materials by adding them to a dispersing apparatus of a three-roll mill; and a fifth process of pasting the fourth raw materials into pastes. (S5), and the sixth step (S6) of measuring and injecting the base raw material and aluminum powder, and the porous silica additive optionally added in this way, in particular.

Conventionally, aluminum powder is added together with a resin, an inorganic binder, and an additive to mix raw materials, but in this case, due to other materials (resin, inorganic binder, and additives) in which aluminum powder, which is composed of fine powder powder, is blended together, The problem is that the bundles are not sufficiently dispersed. Accordingly, in the present invention, the resin, the inorganic binder, and the additive, which are the fine base raw materials, are first blended and sufficiently paste, and the fine aluminum powder powder is mixed therein, so that the aluminum powder is more evenly dispersed, thereby providing more excellent conductivity. Preventing the occurrence of beads and warpage, reducing contact resistance, forming a limited back electrode, and the like.

Subsequently, after the sixth process, a seventh process (S7) of blending the raw material into which the aluminum powder or the like is added again through a mixing machine, and a dispersion device of a three-roll mill for blending the raw material passed through the seventh process An eighth process (S8) of mixing and extruding the blended raw material into and mixing the raw material may be performed, and a ninth process (S9) of measuring the paste material passed through the eighth process to confirm physical properties.

Then, the back electrode material of the raw material mixture prepared as a paste is printed on a silicon wafer and dried, and then sintered to form the back electrode constituting the crystalline solar cell. Can be.

Basically, the composition for preparing a crystalline solar cell back electrode according to the present invention is a mixed composition of an acrylate-based or cellulose-based resin, an aluminum powder, an inorganic binder, and an additive for increasing adhesion to the wafer. Is made of.

First, the acrylate-based or cellulose-based resin in the paste-type back electrode material of the present invention functions to provide fluidity in the screen printing process for forming the front electrode and the back electrode of the crystalline solar cell.

In addition, the aluminum powder provides conductivity to the rear electrode and partially couples with the silicon wafer to form an alloy layer (p +), reduces contact resistance and facilitates formation of the rear electrode.

In particular, the aluminum powder in the present invention and the aluminum powder of 30 ~ 100 nanometers size and It is characterized by a mixture of 2 to 10 microns of aluminum powder.

Conventionally, aluminum powder having a size of 50 to 130 nanometers is used as the aluminum powder. Although a mixture of aluminum powders of 2 to 10 microns in size was used, in the present invention, by using smaller aluminum powders of 30 to 100 nanometers in size, it was confirmed that the series resistance (Rs_contact resistance) value can be further lowered as described below. Thus, the present invention has been completed.

The 30-100 nanometer aluminum powder is preferably an aluminum powder powder having an average particle size of 80 nm, and the present invention can further reduce the series resistance value by using an aluminum powder having a smaller size than the conventional one. Therefore, there is an effect that can have a remarkably excellent photoelectric conversion efficiency (Efficiency).

More specifically, it is possible to use a composition in which an aluminum powder having a size of 30 to 100 nanometers and an average particle size of 2 micron aluminum powder, 4 micron aluminum powder, 6 micron aluminum powder, and 10 micron aluminum powder are mixed.

At this time, the aluminum powder is more preferably made of a mixed composition of 0.01 to 7.0 parts by weight of aluminum powder of 30 to 100 nanometers and 39,9 to 85.0 parts by weight of aluminum powder of 2 to 10 microns. It is preferable to mix the amount a little more by using an aluminum powder of a smaller size than the conventional one.

The content of the above-described aluminum powder, which is composed of a mixed composition of a plurality of particle sizes, prevents the occurrence of beads and warps when forming the back electrode with the paste-type electrode material of the present invention on the wafer, and also has an excellent BSF layer on the wafer. It provides formation and adhesion, and enables stable formation of the back electrode.

The inorganic binder functions to give adhesion to the electrode material of the present invention, which is a paste on the silicon wafer, during printing after printing the electrode material of the present invention for manufacturing a crystalline solar cell.

The inorganic binder is preferably using a glass raw material (Glass Frit), silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ), bismuth oxide (Bi ₂ O ₃ ), Sodium oxide (Na ₂ O), zinc oxide (ZnO) may be made of a compound in which two or more raw materials or a whole are mixed.

The additive is an appropriate value for the effect of improving the antifoam or leveling, dispersion stability and adhesion with the wafer during the printing operation for the production of crystalline solar cells.

The additive is preferably used by selecting any one or two or more of thallium oxide (Tl ₂ O ₃ ), zinc oxide (ZnO), bismuth oxide (Bi ₂ O ₃ ).

In addition, the composition ratio of the raw materials is preferably composed of 40 to 90 parts by weight of aluminum powder, 0.5 to 10 parts by weight of inorganic binder, and 0.1 to 10 parts by weight of additive based on 0.5 to 20 parts by weight of acrylate or cellulose resin.

When the acrylate-based or cellulose-based resin is used in an amount of 0.5 parts by weight or less, it is difficult to perform smooth screen printing when used in the manufacture of solar cells, and in particular, it is difficult to form a uniform film thickness and pattern when printing, and when printing exceeds 20 parts by weight It is difficult to form a precise pattern, such as a large amount of ink dropping during operation, such as bleeding phenomenon, and it causes loss of electrode resistance because it lowers nonvolatile matter and aluminum content during firing.

When the aluminum powder is applied to 40 parts by weight or less, bead (Bead) or BSF (Back Surface Field) layer is difficult to form when used as a back electrode, and when it exceeds 90 parts by weight, the adhesion to the wafer is lowered and warped. This is likely to occur.

When the inorganic binder is used in an amount of 0.5 parts by weight or less, it becomes difficult to express a function for forming adhesion to the wafer during the firing operation for manufacturing a solar cell. When the inorganic binder exceeds 10 parts by weight, the adhesion to the wafer may be increased, but And it acts to increase the contact resistance value of the electrode material, which is a paste, which hinders the flow of electrons formed in the solar cell, thereby lowering the conversion efficiency and causing warpage or bead generation.

In addition, another feature of the present invention may be that the mixed composition further comprises a fumed silica (fumed silica).

Porous silica has a very large specific surface area because it has a porosity, as described later in the present invention by applying such a porous silica to the mixed composition, the conventional bowing (improving) phenomenon is improved.

In order to increase the efficiency of the crystalline solar cell in the trend that the thickness of the wafer gradually becomes thin, the bowing phenomenon should be further reduced without degrading the photoelectric conversion efficiency, the present invention is a mixture further comprising a porous silica (fumed silica) By using the composition, there is an effect that can reduce the bowing phenomenon remarkably superior to the conventional.

At this time, when the porous silica is contained in 0.01 to 10 parts by weight based on 0.5 to 20 parts by weight of the acrylate (acrylate) or cellulose (cellulose) -based resin, it was confirmed that the effect is the most excellent.

On the other hand, Figures 4 to 7 show various experimental results for the composition for producing a back electrode having the above-described configuration of the present invention.

Hereinafter, the prior art in the experimental results means the electrode material according to the Republic of Korea Patent No. 10-0801168 described above or the experimental results for this.

First, Figure 4 is a graph showing an example of the series resistance value (Rs) according to the content of the aluminum powder in the back electrode material prepared according to the present invention and the prior art, respectively.

In the back electrode material according to the present invention, the aluminum powder was mixed with an aluminum powder having a size of 30 to 100 nanometers and an aluminum powder having a size of 2 to 10 microns. In the electrode material according to the prior art, the aluminum powder has a size of 50 to 130 nanometers. The aluminum powder and the aluminum powder of 2 to 10 microns in size were used.

According to the present invention, as shown in Figure 4, it can be seen that the series resistance value is lower than the prior art in the entire content range containing aluminum nano powder, especially aluminum nano powder was included in 6 to 8% by weight When the series resistance value is noticeably low.

5 is a graph showing an example of the series resistance value (Rs) according to the particle size of the aluminum powder in the back electrode material according to the present invention.

In the back electrode material according to the present invention, the aluminum powder was included in an amount of 65 parts by weight based on 10 parts by weight of the acrylate-based or cellulose-based resin, and the aluminum powder was mixed with an aluminum powder having a size of 2-10 microns. The series resistance values were measured while varying the average particle size of the nano-size aluminum powder.

As a result, as shown in Figure 5, when the average particle size is 80nm (when using an aluminum powder of 30 ~ 100nm size) When the average particle size is 100nm (when using an aluminum powder of 50 ~ 130nm size It can be seen that the series resistance value can be lowered better than), and the series resistance value is no longer lowered even if the average particle size is smaller than 80 nm.

Figure 6 is a graph showing the results of bending characteristics according to the printing thickness of the electrode material in each of the back electrode material containing porous silica and the back electrode material not containing porous silica according to the prior art according to the present invention.

Here, the warpage was measured by the thickness of the electrode material, the result of the bowing phenomenon according to this, as shown in Figure 6, compared to the prior art that does not include a porous silica in accordance with the present invention in all sections, warpage phenomenon is significantly You can see the shrinkage.

Figure 7 is a schematic diagram showing the measurement of the light conversion efficiency of the crystalline solar cell using the back electrode material of the present invention.

The table of FIG. 7 calculates the efficiency by measuring voltage and current when artificial sunlight is reflected on the crystalline solar cell to which the present invention is applied.

As shown in the graph of Figure 7, it can be seen that the graph of the present invention located on the right shows better efficiency than the prior art shown on the left.

On the other hand, the present invention has been described with reference to the specific embodiments as described above and the accompanying drawings, but can not be limited to this particular, the implementation of various substitutions, modifications and variations made by those skilled in the art It can be attributed to the technical scope of the present invention by the technical idea according to the interpretation of the claims of the invention.

(Explanation of the sign)

10: silicon wafer 20: antireflection film

30: front electrode 40: rear electrode

The present invention can reduce the series resistance (Rs_contact resistance) value by using an aluminum powder of a smaller size (size) than the conventional, accordingly, the rear surface for manufacturing a high efficiency crystalline solar cell that can have a remarkably excellent photoelectric conversion efficiency An electrode material can be provided.

Claims (6)

In the composition for manufacturing a back electrode used to manufacture a crystalline solar cell in which the front electrode and the back electrode is formed on the front and back of the wafer, It is made up of a mixture of acrylate or cellulose resin, aluminum powder, inorganic binder, and additives to increase adhesion to the wafer. The aluminum powder is an aluminum powder of 30 ~ 100 nanometers A composition for preparing a crystalline solar cell back electrode, characterized in that the aluminum powder of 2 to 10 microns size is mixed. According to claim 1, wherein the aluminum powder is 30 ~ 100 nano-size aluminum powder 0.01 ~ 7.0 parts by weight and 2 ~ 10 micron size aluminum powder 39.9 ~ 85.0 parts by weight of the composition for producing a crystalline solar cell, characterized in that the mixture . The composition of claim 1 or 2, wherein the mixed composition further comprises fumed silica. The crystalline solar cell back electrode of claim 3, wherein the porous silica is comprised in an amount of 0.01 to 10 parts by weight based on 0.5 to 20 parts by weight of an acrylate-based or cellulose-based resin. Composition for preparation. The method according to claim 1 or 2, The inorganic binder is silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ), bismuth oxide (Bi ₂ O ₃ ), sodium oxide (Na ₂ O), zinc oxide (ZnO The composition for preparing a crystalline solar cell back electrode, characterized in that using a glass raw material (Glass Frit) of two or more raw materials or a mixture of all of them. The method according to claim 1 or 2, The additive is tallium oxide (Tl ₂ O ₃ ), zinc oxide (ZnO), bismuth oxide (Bi ₂ O ₃ ) A composition for producing a crystalline solar cell back electrode, characterized in that using any one or two or more.

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