KR101648918B1 - Method for preparation back electrode using Ag paste composition and method for forming silicon solar cell - Google Patents

Abstract

The present invention relates to a silicon solar cell and a method of manufacturing the same, and more particularly, to a method of manufacturing a silicon solar cell and a method of manufacturing the same by using a silver paste composition including a tin powder in forming a back electrode of a silicon solar cell, The present invention relates to a silicon solar cell capable of improving the open circuit voltage by preventing the peeling phenomenon and the twisting phenomenon of the substrate after firing, and a manufacturing method thereof.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a back electrode using a silver paste composition,

The present invention relates to a method of manufacturing a rear electrode using a silver paste composition and a method of manufacturing a silicon solar cell, and more particularly, to a method of manufacturing a back electrode using a silver paste composition including a tin powder together with an aluminum paste composition, A method of fabricating a back electrode capable of easily forming an Ag pattern on the Ag layer and preventing the Ag pattern from cracking and also preventing warping between Ag and aluminum to improve the electrical characteristics of the solar cell with an increase in open circuit voltage, And a method for producing the same.

Recently, as electronic industry has developed, miniaturization and high reliability of electronic products and devices have been demanded. Various methods have been tried to form circuit patterns and electrodes of electronic products requiring high integration. Among them, the use of a conductive metal paste is a subject of interest because there is little generation of by-products and contaminants in the process.

The metal paste generally used includes a conductive metal, a glass frit, and an organic binder. As the conductive metal, silver, aluminum, or the like is used. Among them, silver is mainly used. At present, conductive metal paste is mainly used for hybrid IC, semiconductor IC mounting and various capacitors and electrodes. Recently, it is widely used in high-tech electronic products such as PCB, EL, touch panel, RFID, LCD, PDP, As the related industries are expanded and developed, the demand is also increasing.

For example, in the case of photovoltaic cells, there is a growing interest in alternative energy sources, as existing energy resources such as oil and coal are expected to be depleted. Among them, solar cells are rich in energy resources and have no problems with environmental pollution Especially noteworthy.

Solar cells are divided into solar cells that generate the steam needed to rotate the turbine using solar heat, and solar cells that convert sunlight (photons) into electrical energy using the properties of semiconductors. Solar photovoltaic cells (hereinafter referred to as solar photovoltaic).

Solar cells are divided into silicon solar cell, compound semiconductor solar cell and tandem solar cell according to raw materials. Of these three types of solar cells, silicon solar cells are the mainstream in the solar cell market.

1 is a cross-sectional view showing a basic structure of a silicon solar cell. Referring to the drawings, a silicon solar cell includes a substrate 101 made of a p-type silicon semiconductor and an emitter layer 102 made of an n-type silicon semiconductor, and a diode 101 is formed at the interface between the substrate 101 and the emitter layer 102. [ A pn junction is formed. In addition, the substrate made of the p-type silicon semiconductor includes a back surface field (BSF) layer for lowering the contact resistance with the back electrode and improving the characteristics of the solar cell. The front electrode of the solar cell has Ag formed on the front surface of the substrate and conductive aluminum and silver on the rear surface. At this time, although the front electrode is not shown in the drawing, it is connected to the emitter layer through the antireflection film when the silicon solar cell is formed.

When sunlight enters the solar cell having the above structure, electrons and holes are generated in a silicon semiconductor doped with impurities by a photovoltaic effect. For reference, electrons are generated in a majority carrier in the emitter layer 102 made of an n-type silicon semiconductor, and holes are generated in a majority carrier in the substrate 101 made of a p-type silicon semiconductor. Electrons and electrons generated by the photovoltaic effect are attracted toward the n-type silicon semiconductor and the p-type silicon semiconductor, respectively, and are electrically connected to the front and back electrodes 103 and 104 bonded to the bottom of the substrate 101 and the top of the emitter layer 102, When the electrodes 103 and 104 are connected by a wire, a current flows.

Conductive metal pastes are used for the production of front or rear electrodes in solar cells and are used to manufacture various electrodes in other electronic products as described above.

On the other hand, in the case of a back electrode of a silicon solar cell, an aluminum film 106 for forming an aluminum electrode on a substrate 101 made of a p-type silicon semiconductor and a predetermined Ag pattern (107).

2 is a cross-sectional view schematically showing a front view (a) of a back electrode and a manufacturing process (b) of a back electrode using a conventional silver paste composition for forming a back electrode.

2 (b), the rear electrode is printed and fired in a predetermined pattern on a substrate 101 made of a p-type silicon semiconductor using a normal silver paste composition to form an Ag pattern 107 And the aluminum paste composition is printed and fired between predetermined Ag patterns 107 to produce the back electrode 105 including the aluminum film 106. [

However, as the thickness of the BSF layer is increased, the performance of the solar cell is improved. In the case of the conventional method, the BSF layer is not formed well, resulting in a decrease in the open circuit voltage. That is, as shown in FIG. 2 (b), after the firing of the aluminum paste, the Ag pattern melts down to the state a and the back surface field (BSF) layer formed on the back surface of the silicon semiconductor substrate And the effect of aluminum is deteriorated. Accordingly, a problem that the open-circuit voltage is reduced by 4 to 6 mV compared with the thick-film printing is caused by the Ag pattern of the thick film. Also, when silver paste is used to form an Ag pattern on the rear electrode, warpage and peeling phenomenon between Ag and aluminum occur after baking due to the difference in thermal expansion coefficient between the paste and the aluminum paste.

Generally, it is possible to form an Al pattern on an Ag film, but it is difficult to form an Ag pattern on an Al film. The reason for this is that since the thermal expansion rate of Al is large, after the sintering process and after cooling, the Ag pattern on the aluminum film cracks and is torn out.

It is an object of the present invention to provide a silver paste composition containing a tin powder in the formation of a back electrode of a solar cell to prevent twisting and peeling between Ag and aluminum without cracking of the Ag pattern, Can be minimized, thereby improving the electrical characteristics of the solar cell, and a method of manufacturing the same.

Forming an aluminum film having a predetermined thickness by applying an aluminum paste composition to a back surface of a first conductivity type semiconductor substrate on which an emitter layer and an antireflection film are formed;

Printing a silver paste composition including silver powder, tin powder, glass frit powder, and an organic binder on an aluminum film formed on the substrate to form an Ag pattern; And

Simultaneously firing the aluminum film and the substrate having the Ag pattern;

Wherein the back electrode is formed on the back electrode.

The tin powder preferably has a thermal expansion coefficient of 21 x 10 ^-6 / 캜, a thermal conductivity of 66.8 (W / mk, 25 캜) and an average particle diameter of 0.1 탆 to 10 탆. The tin powder may be contained in an amount of 1 to 20 parts by weight based on 100 parts by weight of the silver powder.

The calcination is carried out at a temperature of from room temperature to 1,000 ° C for several seconds to several minutes, preferably for a time of from 5 seconds to 3 minutes or less. The step of firing may include a step in which the Ag pattern penetrates the aluminum film to form a predetermined Ag / Al pattern.

According to the present invention, there is also provided a method of manufacturing a semiconductor device, comprising: (a) forming an emitter layer on a first conductivity type semiconductor substrate;

(b) forming an antireflection film on the emitter layer; And

(c) forming a front electrode on the antireflection film in a predetermined pattern, and

(d) forming a rear electrode on the rear surface of the first conductivity type semiconductor substrate by the method described above;

The present invention provides a method of manufacturing a silicon solar cell.

According to the present invention, by using a silver paste composition containing tin powder together with an aluminum paste composition in forming a back electrode of a silicon solar cell, it is possible to easily form an Ag pattern on an aluminum film, There is no peeling phenomenon due to an improvement in adhesion between aluminum and silver, and warping between Ag and aluminum formed on the substrate is prevented, thereby improving the open circuit voltage. Further, the present invention has the effect of improving the electrical characteristics of the solar cell by reducing the interface resistance between the substrate and the electrode by the tin powder. In addition, according to the present invention, the amount of silver used can be reduced by replacing a part of the silver used for the rear electrode with tin, thereby coping with an increase in the price of silver powder, which is economical.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given above, serve to further the understanding of the technical idea of the invention, And should not be construed as limiting.
1 is a cross-sectional view showing a schematic structure of a conventional silicon solar cell.
2 is a cross-sectional view schematically showing a front view (a) of a back electrode and a manufacturing process (b) of a back electrode using a conventional silver paste composition for forming a back electrode.
3 is a cross-sectional view schematically showing a front view (a) of a back electrode and a manufacturing process (b) of a back electrode using a silver paste composition for forming a back electrode of the present invention.
4 is a schematic diagram of a solar cell manufactured according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The present invention relates to a method of easily forming an Ag pattern on an aluminum film of a rear electrode using a silver paste composition comprising conductive tin powder as an additive in forming a back electrode, and a method of manufacturing a silicon solar cell using the method. Accordingly, it is an object of the present invention to provide a method of manufacturing a back electrode that can improve the light conversion efficiency of a solar cell, and a method of manufacturing a silicon solar cell using the same.

That is, the method of the present invention can solve the twist phenomenon between the Ag and the aluminum film after firing by adding tin (Sn) having an intermediate thermal expansion coefficient to the silver paste in order to reduce the thermal expansion coefficient of Ag and aluminum.

Hereinafter, a method of manufacturing a rear electrode and a method of manufacturing a silicon solar cell according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIGS. 3 and 4 are cross-sectional views schematically illustrating the structure of a silicon solar cell manufactured using the rear electrode according to a preferred embodiment of the present invention. It is to be understood, however, that the present invention is not limited to the embodiments described herein, and that the present invention is not limited thereto. It should be understood that various equivalents and modifications may be present.

First, a method of manufacturing a rear electrode according to a preferred embodiment of the present invention includes: forming an aluminum film having a predetermined thickness by applying an aluminum paste composition to a rear surface of a first conductivity type semiconductor substrate; Printing a silver paste composition including silver powder, tin powder, glass frit powder, and an organic binder on an aluminum film formed on the substrate to form an Ag pattern; And simultaneously firing the aluminum film and the substrate having the Ag pattern.

Further, the step of firing may include a step in which the Ag pattern penetrates the aluminum film to form a predetermined Ag / Al pattern. The firing can be carried out at a temperature of from room temperature to 1,000 DEG C for a few seconds to several minutes, preferably, from 5 seconds to 3 minutes or less. At this time, in the case of the present invention, in the firing process, the temperature may be raised to a temperature within a range of from room temperature to 1000 ° C, followed by firing. The first conductive semiconductor substrate may be a p-type silicon substrate.

More specifically, FIG. 3 is a cross-sectional view schematically showing a front view (a) of a back electrode using a silver paste composition for forming a back electrode of the present invention and a manufacturing process (b) of a back electrode.

Referring to FIG. 3, the rear electrode 205 is printed on the lower surface of the substrate 201 using a silver paste together with an aluminum paste for the rear electrode to which aluminum, quartz silica, a binder and the like are added, do. Aluminum may be diffused through the lower portion of the substrate 201 to form a back surface field (not shown) at the interface between the rear electrode 205 and the substrate 201 during the heat treatment of the rear electrode have. When the rear-front layer is formed, the carrier can be prevented from moving to the lower portion of the substrate 201 and recombining. When the recombination of the carriers is prevented, the open voltage and the fidelity are increased and the conversion efficiency of the solar cell is improved.

In this method of the present invention, an emitter layer and an antireflection film are formed on a first conductivity type semiconductor substrate 201 by a conventional method, and an aluminum paste is applied to a back surface of the semiconductor substrate 201 to a predetermined thickness to form an aluminum film 206 are formed.

That is, according to the present invention, a substrate 201 made of a silicon semiconductor doped with an impurity of a first conductivity type is prepared and loaded into a diffusion furnace. Here, the substrate 201 is a monocrystalline, polycrystalline or amorphous silicon semiconductor, and is doped with a p-type impurity such as B, Ga or In, which is a group III element. Next, an n-type impurity source such as P, As, Sb, or the like, which is a Group 5 element, is implanted together with oxygen gas in the diffusion furnace to cause a thermal oxidation reaction to form an oxide film containing n-type impurities on the upper surface of the substrate 201 . Then, the temperature of the diffusion furnace is raised to 800 to 900 캜 to drive-in the n-type impurity contained in the oxide film to the upper surface of the substrate 201. At this time, the diffusion time is maintained for 30 to 60 minutes so that a sufficient amount of the n-type impurity is diffused into the substrate 201. Then, the n-type impurity contained in the oxide film is diffused into the substrate 201 through the surface of the substrate 201, thereby forming an emitter layer 202 of an n-type silicon semiconductor layer with a constant thickness on the substrate 201.

The concentration of the n-type impurity injected into the emitter layer through the diffusion process of the n-type impurity is highest at the surface of the emitter layer and decreases with increasing Gaussian distribution or error function as it enters the emitter layer. Since the process conditions are adjusted so that a sufficient amount of the n-type impurity is diffused during the diffusion process, a dead layer doped with the n-type impurity is present in the uppermost layer of the emitter layer at a concentration higher than the solubility of the solid solution.

Since the emitter layer formation process disclosed in the embodiment of the present invention is only one embodiment, it is apparent that the emitter layer formation process can be replaced with various known processes known in the art.

In this way, when the substrate 201 and the emitter layer are doped with an impurity of the opposite conductivity type, a p-n junction is formed at the interface between the substrate 201 and the emitter layer. The p-n junction may be formed by doping the substrate 201 with an n-type impurity and doping the emitter layer with a p-type impurity.

When the emitter layer is formed through the above-described processes, a defect (for example, a dangling bond) existing in the surface or bulk of the emitter layer is immobilized on the emitter layer, and a reflectance Thereby forming an antireflection film. At this time, if the defect existing in the emitter layer is passivated, the recombination site of the minority carriers is removed and the open circuit voltage of the solar cell is increased. If the reflectivity of sunlight decreases, the amount of light reaching the pn junction increases, and the short circuit current of the solar cell increases. As the open-circuit voltage and the short-circuit current of the solar cell are increased by the antireflection film, the conversion efficiency of the solar cell is improved accordingly. The antireflection film may be formed of any one single film selected from the group consisting of a silicon nitride film, a silicon nitride film including hydrogen, a silicon oxide film, a silicon oxynitride film, MgF ₂ , ZnS, MgF ₂ , TiO ₂ and CeO ₂ , So as to have a multi-film structure. The antireflection film is formed by vacuum deposition, chemical vapor deposition, spin coating, screen printing or spray coating. However, the present invention is not limited by the structure and the formation method of the antireflection film.

When the formation of the antireflection film is completed, an aluminum paste is applied to the lower portion of the substrate 201 by an ordinary method such as a screen printing method to form an aluminum film.

Next, a silver paste containing tin powder according to the present invention is printed on the aluminum film 206 in a predetermined pattern to form an Ag pattern 207.

Next, the aluminum film 206 and the semiconductor substrate including the Ag pattern 207 are simultaneously baked.

When the aluminum film 206 and the first conductivity type semiconductor substrate printed with the Ag pattern 207 are simultaneously fired, the tin powder in the composition containing the Ag pattern reduces the thermal expansion coefficient value, and the tin powder and the silver powder are mixed with the aluminum paste Flows through the pores to reach the interface. In addition, the glass frit component melts the silver powder in the Ag pattern and penetrates the aluminum film to form a predetermined Ag / Al pattern, and a BSF layer, which is a p + layer, may be formed between the silver foil component and the substrate. Accordingly, the back electrode 205 including the aluminum film 206 and the Ag / Al pattern 208 is formed on the semiconductor substrate through the firing process.

At this time, in the step of forming the rear electrode, the firing conditions are not particularly limited, but it is preferable that the firing is performed for a few seconds to several minutes at a temperature within a range of from room temperature to 1,000 deg.

The first conductivity type semiconductor substrate on which the emitter layer and the antireflection film are formed is a p-type silicon substrate,

As described above, according to the present invention, silver paste for forming Ag of the aluminum paste and the rear electrode is sequentially formed on the substrate, and then the substrate is fired at the time of forming the rear electrode, so that the aluminum paste and the silver paste are simultaneously fired, The tin powder and silver powder contained in the silver paste of the silver paste flow into the gap between the aluminum paste and partially reach the interface of the silicon substrate. In this way, there is no warping between the Ag pattern and the aluminum film, and there is no detachment, so that the aluminum printing can be performed all over the surface, and the decrease of the open-circuit voltage (Voc) can be remarkably lowered to the level of 1 to 2 mV.

Meanwhile, in the case of the silver (Ag) paste composition for forming the Ag pattern of the back electrode of the present invention used in the formation of the back electrode, silver powder, glass frit and organic binder are included. In order to increase the efficiency of the solar cell, and a 21x10 ^-6 / ℃, characterized in that the thermal conductivity comprises 66.8 (W / mk, 25 ℃ ) and the average particle diameter to 0.1㎛ 10㎛ the conductive tin powder.

Since the conductive tin powder has a thermal expansion coefficient higher than that of silver (19 x 10 ^-6 / ° C) commonly used in silver paste compositions and lower than aluminum (23 x 10 ^-6 / ° C), the tin powder The silver powder may partially reach the interface of the substrate with tin powder and silver powder to the interface of the substrate after flowing the powder between the pores in the aluminum paste. Therefore, there is no problem that the Ag pattern and the aluminum are twisted as in the conventional method, and no crack occurs. In addition, tin powder can be used as a substitute for silver since the melting point is lower than that of silver powder and electrons can be discharged to provide a path for electron transfer in the electrode. Further, the tin powder can improve the adhesive force and reduce the amount of glass frit used. Therefore, the present invention can reduce the decrease of the open-circuit voltage and manufacture the silicon solar cell economically.

The content of the conductive tin powder may be suitably used. For example, it is preferably 1 to 20 parts by weight, more preferably 5 to 15 parts by weight, and most preferably 5 to 15 parts by weight based on 100 parts by weight of the silver powder. 10 parts by weight. If the content of the conductive tin powder is less than 5 parts by weight, there is a problem that the adhesion of Ag to Al is weak. Also, when the tin powder is contained in an amount of 20 parts by weight or more, the overall resistivity of the Ag electrode as the thick film electrode drops to 10 ^-6 or less, resulting in an insufficient flow of electric current, thereby deteriorating the cell efficiency.

In addition, in the silver paste composition of the present invention, tin is used for replacing Ag components, but it is not necessary to prevent recrystallization of Ag. Therefore, the rate at which tin is melted and flows into the interface can be controlled by controlling the silver particle size. When silver particles are used only as a large particle, the particle size of the silver powder is important and the adjustment of the tap density is also necessary because the tin quickly enters the interface through the voids between the particles. Therefore, it is preferable that the silver powder used in the present invention has an average particle diameter of 0.1 to 10 mu m and a tap density of 2 to 7 g / cm < ³ >.

The total amount of the silver powder is preferably 50 to 80% by weight, more preferably 60 to 70% by weight based on the paste composition. When the content of the silver powder is less than 50% by weight, there is a problem that the resistivity is lowered. When the content is more than 80% by weight, there is little change in the resistivity.

The glass frit powder that can be used in the present invention can be used without limitation as the glass frit used in the art. Examples of such glass frit powders may include lead oxides and / or bismuth oxides. Specifically, SiO _{2 -PbO-based, SiO 2 -PbO-B 2 O} 3 _{type, Bi 2 O 3 -B 2 O} 3 -SiO 2 series, or a _{PbO-Bi 2 O 3 -B 2} O 3 -SiO 2 based Powder, etc. may be used alone or in combination of two or more, but the present invention is not limited thereto.

The organic binder is used to prepare silver powder, glass frit, and plasticizer as a paste. The organic binder used in the present invention may be any organic binder used in the art to prepare the paste composition. For example, the organic binder may be any one or a mixture of two or more selected from the group consisting of cellulose resin, acrylic resin, butyl carbitol and terpineol, but is not limited thereto. Preferably, ethyl cellulose or acryl A polymer resin of a rate series can be used.

The content of the glass frit and the organic binder is in a range that can easily form an electrode, has a very easy viscosity for screen printing, can prevent a paste from flowing down after screen printing and can exhibit an appropriate aspect ratio, The range is not particularly limited.

For example, the content of the glass frit as a whole is preferably 0.5 to 6% by weight, more preferably 1 to 5% by weight, and most preferably 2 to 4% by weight based on the paste composition. If the content of the glass frit is less than 0.5 wt%, there is a problem that the adhesion force of the Ag electrode is weakened. When the content is more than 6 wt%, the line resistance and the resistivity can be increased by the glass frit.

The content of the organic binder is preferably 15 to 30% by weight, more preferably 20 to 25% by weight based on the paste composition. If the content of the organic binder is less than 15% by weight, the adhesive properties are insufficient and the paste components are not easily mixed. Also, the adhesive strength to the substrate due to the use of the organic binder can not be sufficiently obtained. When the content exceeds 30% by weight, The burn out of the paste composition may be difficult.

The silver paste composition of the present invention can be obtained by mixing in various ways known in the art so that the respective components are uniformly dispersed.

Alternatively, the silver paste compositions of the present invention may further comprise additional additives within the scope of the present invention. For example, conductive metal particles, antifoaming agents, dispersants, plasticizers and the like may be further added to the composition of the present invention as needed. The silver paste composition of the present invention may further comprise an organic solvent.

A method for producing the silver paste composition of the present invention will be described below. Basically, it is possible to manufacture a paste using a method in which silver powder, glass frit powder, binder and the conductive tin-based powder are simultaneously mixed and mixed. Mixing of the components can be uniformly carried out using a three roll mill or the like.

In the present invention, the aluminum paste composition may include aluminum powder, glass frit, an organic solvent, and an organic binder, and each component may be a commonly known one, and the kind and content thereof are not particularly limited. For example, the glass frit, organic solvent, and organic binder may be the same as those used in the silver paste composition. Aluminum powders may also be used in common.

Hereinafter, a silicon solar cell using a rear electrode manufactured using the silver paste composition of the present invention and a method of manufacturing the same will be described with reference to FIG.

A method of manufacturing a silicon solar cell according to a preferred embodiment of the present invention includes:

(a) forming an emitter layer on a first conductivity type semiconductor substrate;

(b) forming an antireflection film on the emitter layer; And

(c) forming a front electrode on the antireflection film in a predetermined pattern, and

(d) forming a rear electrode on the back surface of the first conductivity type semiconductor substrate in the above-described manner.

The step of forming the front electrode may include printing and firing a front electrode forming paste in a predetermined pattern on the antireflection film and connecting the front electrode to the emitter layer through the antireflection film.

That is, in the present invention, a substrate 201 made of a silicon semiconductor doped with an impurity of the first conductivity type is prepared in the same manner as in the formation of the rear electrode, and then an n-type silicon semiconductor layer The emitter layer 202 is formed.

Specifically, the present invention provides a substrate 201 made of a silicon semiconductor doped with an impurity of a first conductivity type used in the fabrication of the rear electrode, and is loaded into a diffusion furnace. Next, an n-type impurity source such as P, As, Sb, or the like, which is a Group 5 element, is implanted together with oxygen gas in the diffusion furnace to cause a thermal oxidation reaction to form an oxide film containing n-type impurities on the upper surface of the substrate 201 . Then, the temperature of the diffusion furnace is raised by 800 to 900 degrees to drive-in the n-type impurity contained in the oxide film to the upper surface of the substrate 201. At this time, the diffusion time is maintained for 30 to 60 minutes so that a sufficient amount of the n-type impurity is diffused into the substrate 201. Then, the n-type impurity contained in the oxide film is diffused into the substrate 201 through the surface of the substrate 201, thereby forming an emitter layer 202 of an n-type silicon semiconductor layer with a constant thickness on the substrate 201.

The concentration of the n-type impurity implanted into the emitter layer 202 through the diffusion process of the n-type impurity is highest at the surface of the emitter layer 202 and increases toward the Gaussian distribution or error function as it enters the emitter layer 202 . Since the process conditions are adjusted so that a sufficient amount of the n-type impurity is diffused in the diffusion process, a dead layer doped with the n-type impurity is present in the uppermost layer of the emitter layer 202 at a concentration higher than that of the solid solubility.

It is obvious that the emitter layer formation process disclosed in the embodiment of the present invention is only one embodiment, and therefore, the process of forming the emitter layer 202 can be replaced with various known processes known in the art.

When the substrate 201 and the emitter layer 202 are doped with an impurity of the opposite conductivity type in this manner, a p-n junction is formed at the interface between the substrate 201 and the emitter layer 202. The p-n junction may be formed by doping the substrate 201 with an n-type impurity and doping the emitter layer 202 with a p-type impurity.

When the emitter layer 202 is formed through the above-described processes, defects existing in the surface or bulk of the emitter layer (for example, dangling bonds) are immobilized on the emitter layer 202 to reduce the reflectance of sunlight incident on the front surface of the substrate The antireflection film 203 is formed. At this time, if defects present in the emitter layer 202 are passivated, the recombination sites of the minority carriers are removed and the open-circuit voltage of the solar cell increases. If the reflectivity of sunlight decreases, the amount of light reaching the pn junction increases, and the short circuit current of the solar cell increases. When the open-circuit voltage and the short-circuit current of the solar cell are increased by the antireflection film 203, the conversion efficiency of the solar cell is improved accordingly. The antireflection film 203 may be formed of any one single film selected from the group consisting of a silicon nitride film, a silicon nitride film including hydrogen, a silicon oxide film, a silicon oxynitride film, MgF ₂ , ZnS, MgF ₂ , TiO ₂ and CeO ₂ , Film is formed to have a combined multi-film structure. The antireflection film 203 is formed by vacuum deposition, chemical vapor deposition, spin coating, screen printing, or spray coating. However, the present invention is not limited by the structure and the formation method of the anti-reflection film 203.

After the formation of the emitter layer 202, an etching mask pattern (not shown) is formed at a connection point of the front electrode 204 over the emitter layer 202 doped with the n-type impurity using a normal screen printing method . In addition, an etch-back process can be performed on the emitter layer as needed, and a selective etching layer can be formed by removing the etching mask pattern remaining on the substrate surface.

Then, when the formation of the antireflection film 203 is completed, the front electrode 204, which is an upper electrode, and the rear electrode 205, which is a lower electrode, are connected to the upper portion of the emitter layer 202 and the lower portion of the substrate 201, respectively. The front electrode 204 may be formed by a variety of known techniques, but may be formed by a screen printing method. That is, the front electrode 204 is formed by screen printing a front electrode paste to which silver (Ag), glass frit, and a binder are added to the front electrode formation point of the emitter layer, and then performing heat treatment. When the heat treatment is performed, the front electrode 204 is connected to the emitter layer 202 through the anti-reflection film 203 by a punch through phenomenon. Particularly, the rear electrode completes the structure of the silicon solar cell by forming the rear electrode on the back surface of the first conductivity type semiconductor substrate in which the emitter layer and the antireflection film are formed, according to the method of the present invention described above.

In the present invention, the method of printing the paste for forming the front electrode 204 and the rear electrode 205 may be formed using a conventional photolithography process and a metal deposition process in addition to the screen printing process. In the present invention, the printing method for forming the front electrode and the rear electrode may be a conventional method such as the above-described doctor blade, inkjet printing, and gravure printing. Therefore, the present invention is not limited by the process applied for the formation of the front electrode 204 and the rear electrode 205.

4, the silicon solar cell according to the present invention includes a silicon semiconductor substrate 201, an emitter layer 202 formed on the substrate 201, An antireflection film 203 formed on the emitter layer 202, a front electrode 204 connected to the upper surface of the emitter layer 202 through the antireflection film 203, And a backside electrode 205 manufactured by the method according to the present invention connected to the backside electrode 205. The photovoltaic conversion open-circuit voltage of the silicon solar cell manufactured by the above method may be 0.625 to 0.634 V.

Best Mode for Carrying Out the Invention Hereinafter, the function and effect of the present invention will be described in more detail through a specific embodiment of the present invention. It is to be understood, however, that these embodiments are merely illustrative of the invention and are not intended to limit the scope of the invention.

< Comparative Example  1 and Example  1 to 4>

The silver paste compositions were prepared by mixing the respective components according to the composition and contents shown in Table 1 below (unit: wt%).

Silver powder having an average particle diameter of 3 mu and tin particles having an average particle diameter of 2 mu were used. Glass frit having an average particle diameter of 2 mu containing bismuth oxide was used, and ethyl cellulose was used as the organic binder. Table 2 shows the properties of silver and tin.

Silver powder
(weight%) Glass frit
(weight%) Organic binder
(weight%) additive ingredient Content (% by weight) Example 1 70 2 24.5 Sn 3.5 Example 2 67 2 24.5 Sn 6.5 Example 3 63 2 24.5 Sn 10.5 Example 4 60 2 24.5 Sn 13.5 Comparative Example 1 73.5 2 24.5 - -

Ag Sn Specific gravity (20 ℃) 10.5 7.35 CT, E (x 10 ^-6 / ° C) 19 21 Thermal conductivity (W / mk, 25 ° C) 426 66.8 Resistivity (x 10 ^-6 Ωcm) 1.6 11 Melting point (℃) 961 231 Boiling point (℃) 2162 2602

< Example  5-8>

To fabricate the silicon solar cell of FIG. 3, the back electrode was fabricated using the method of FIG.

That is, the silicon semiconductor substrate 201 was prepared, and an emitter layer, an antireflection film, and a front electrode were formed by a normal method.

Next, an aluminum paste composition containing aluminum powder, glass frit, ethyl cellulose and terpineol was applied to the back surface of the substrate 201 by a screen printing method to a thickness of 10 to 30 占 according to the method of Fig. Thereafter, the silver paste compositions prepared in Examples 1 to 4 were coated on the applied film in a predetermined pattern, respectively (thickness: 20 to 30 mu m). Then, the substrate was heated at a temperature of 900 ° C at room temperature to form a rear electrode 205 including an aluminum film 207 and a predetermined Ag / Al pattern 208 on the substrate 201.

An emitter layer 202 and an antireflection film 203 are sequentially formed on the substrate 201 and the emitter layer 202 through the antireflection film 203 And a rear electrode 205 connected to the back surface of the substrate 201 and having a predetermined Ag pattern through the aluminum layer to form an Ag / Al pattern, (Examples 5 to 8). &Lt; tb &gt;&lt; TABLE &gt;

< Comparative Example  2>

A silicon solar cell was produced in the same manner as in Example 5, except that a conventional aluminum paste and a silver paste of Comparative Example 1 were used to form the rear electrode according to the method of Fig.

< Experimental Example >

The properties of the silicon solar cells of Examples 5-8 and Comparative Example 2 were measured by a conventional method, and the results are shown in Table 3.

Adhesion Resistivity (x 10 ^-6 Ωcm) Voc (V) Example 5 △ 6.4 0.632 Example 6 ○ 9.6 0.631 Example 7 ○ 14 0.629 Example 8 △ 23 0.627 Comparative Example 2 × 3.4 0.629 Note) Adhesion evaluation standard
?: 1 to 2 N / mm
?: 0.5 to 1 N / mm
X: 0.5 N / mm or less

As shown in Table 3, Examples 5 to 8 of the present invention show that the silver paste composition containing tin powder having a high specific resistance has excellent adhesion and electric characteristics (open-circuit voltage) have.

On the other hand, when the conventional silver paste composition of Comparative Example 1 was used, the open-circuit voltage was low even when the open-circuit voltage reached a certain level, and the resistivity dropped to 10 &lt; ^-6 &gt; As a result, in Comparative Example 2, the current flow was not smooth and the cell efficiency dropped.

101, 201: substrate 102, 202: emitter layer
103, 203: antireflection film
204: front electrode 105, 205: rear electrode
106, 206: Aluminum film 107: Ag pattern
207: Ag pattern 208: Ag / Al pattern

Claims (13)

Forming an aluminum film having a predetermined thickness by applying an aluminum paste composition to the back surface of the first conductivity type semiconductor substrate having the emitter layer and the antireflection film formed thereon;
Printing a silver paste composition including silver powder, tin powder, glass frit powder, and an organic binder on an aluminum film formed on the substrate to form an Ag pattern; And
Simultaneously firing the aluminum film and the substrate having the Ag pattern;
/ RTI &gt;
The tin powder has a thermal expansion coefficient of 21x10 &lt; ^-6 &gt; / DEG C, a thermal conductivity of 66.8 (W / mk, 25 DEG C), an average particle diameter of 0.1 mu m to 10 mu m,
Wherein the silver powder has an average particle diameter of 0.1 mu m to 10 mu m and a tap density of 2 to 7 g / cm &lt; ³ &gt;. delete The method according to claim 1, wherein the tin powder is contained in an amount of 1 to 20 parts by weight based on 100 parts by weight of the silver powder. delete The method of claim 1, wherein the firing is performed at a temperature within a range of from room temperature to 1,000 ° C for a time within a range of 5 seconds to 3 minutes. 2. The method of claim 1, wherein the step of firing includes the step of forming an Ag / Al pattern through the Ag pattern by penetrating the aluminum film. The method of claim 1, wherein the first conductivity type semiconductor substrate is a p-type silicon substrate. 2. The method of claim 1, wherein the aluminum paste composition comprises aluminum powder, glass frit, an organic solvent and an organic binder. The method of claim 1 or 8, wherein the glass frit powder comprises lead oxide or bismuth oxide. The method according to claim 1 or 8, wherein the organic binder is any one or a mixture of two or more selected from the group consisting of a cellulose resin, an acrylic resin, butyl carbitol, and terpineol. The method of claim 1, wherein the silver paste composition further comprises an organic solvent. (a) forming an emitter layer on a first conductivity type semiconductor substrate;
(b) forming an antireflection film on the emitter layer; And
(c) forming a front electrode on the antireflection film in a predetermined pattern, and
(d) forming a rear electrode on the back surface of the first conductivity type semiconductor substrate by the method according to claim 1;
&Lt; / RTI &gt; The method according to claim 12, wherein the step of forming the front electrode includes printing and firing a front electrode forming paste in a predetermined pattern on the antireflection film and connecting the front electrode to the emitter layer through the antireflection film Wherein the method comprises the steps of:

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