KR101371865B1 - Front electrode structure of solar cell and fabricating method thereof - Google Patents

Abstract

Disclosed are the structure of a front electrode of a solar cell and a method for manufacturing the same. In the structure of a front electrode of a solar cell which includes a finger line electrode and a bus bar electrode, a plating electrode including copper (Cu), specifically, a plating electrode consisting of an alloy of nickel (Ni), copper (Cu) and tin (Sn) or of an alloy of nickel (Ni), copper (Cu) and silver (Ag), is applied to the finger line electrode. In addition, as the bus bar electrode requires stronger adhesiveness compared with the plating electrode due to the soldering of a ribbon, a metal paste strongly adhering to a silicon interface is applied to the bus bar electrode. As the amount of silver (Ag), which is expensive, is less used in the manufacturing process of the front electrode, manufacturing costs can be reduced, and high efficiency can be achieved. Also, an adhesion property with a silicon interface can be improved.

Description

Front electrode structure of solar cell and manufacturing method thereof {Front electrode structure of solar cell and fabricating method

The present invention relates to solar cell technology, and more particularly, to a front electrode structure of a solar cell and a method of manufacturing the same.

A solar cell is a key element of photovoltaic power generation that directly converts sunlight into electricity and is basically a diode composed of a p-n junction. In the process of converting sunlight into electricity by solar cells, when solar light is incident on a silicon solar cell substrate, electron-hole pairs are generated, and electrons move to n layers and holes move to p layers by an electric field. Thus, photovoltaic power is generated between the pn junctions. At this time, if a load or a system is connected to both ends of the solar cell, a current flows to generate power.

Looking at the structure of a typical solar cell, a doping layer having a predetermined depth is formed on the upper layer of the front surface of the substrate, the anti-reflection film is provided to cover the region of the doped layer except the electrode region, the front surface on the electrode region of the substrate front and the back of the substrate The electrode and the back electrode are each provided with a structure.

Among them, the front electrode of the solar cell is configured in detail with a plurality of finger lines and a bus bar connecting them with each other. The fingerline is evenly disposed on the front surface of the solar cell to collect photoelectrically converted charges, and the busbar serves to transport the carriers collected by the fingerline to the outside. On the busbar is provided a conductive interconnector, or ribbon, for electrical connection with adjacent solar cells.

Silver (Ag) paste may be used to form the front electrode. However, if the silver (Ag), which is an expensive metal, is used entirely, manufacturing cost increases are inevitable.

Accordingly, in recent years, solar cells using a plating electrode using a metal such as copper (Cu), which replaces an expensive silver (Ag) electrode, have been developed for cost reduction.

However, when the front electrode of the solar cell is formed of a plating electrode, the adhesion between the silicon interface, which is the surface of the solar cell, and the plating electrode is weak, so that the adhesive strength evaluation after soldering the ribbon does not meet the standard value. have.

Korea Patent Registration No. 10-1138174

The present invention has been proposed in order to solve the problems of the prior art as described above, using a low-cost material to achieve a cost reduction and efficiency, and at the same time, a front electrode structure of a solar cell and a stable adhesive property can be implemented The purpose is to provide a manufacturing method.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the precise form disclosed. There will be.

The front electrode structure of the solar cell according to the present invention is a silicon solar cell substrate; A plurality of fingerline electrodes formed on the front surface of the substrate; And a busbar electrode formed on the front surface of the substrate to connect the plurality of fingerline electrodes to each other, wherein the busbar electrode includes a metal paste layer, and the plurality of fingerline electrodes include a plating layer. It is done.

The metal paste layer of the busbar electrode may be formed by applying and firing silver (Ag) paste or by applying and firing copper (Cu) paste.

When using a copper (Cu) paste, the busbar electrode may further include a surface plating layer on the copper (Cu) paste layer.

The plating layers of the plurality of fingerline electrodes sequentially form nickel (Ni) / copper (Cu) / tin (Sn), or nickel (Ni) / copper (Cu) / silver (Ag) from the silicon interface of the solar cell substrate. It can be formed by plating.

Method for manufacturing a solar cell front electrode structure according to the present invention comprises the steps of preparing a solar cell substrate; Forming a plurality of fingerline electrodes including a plating layer on a front surface of the solar cell substrate through a plating process; And forming a busbar electrode including a metal paste layer connecting the plurality of fingerline electrodes to each other by applying and firing a metal paste for forming a busbar electrode on a front surface of the substrate on which the plurality of fingerline electrodes are formed. Characterized in that it comprises a step.

The metal paste layer of the busbar electrode may be formed by applying and firing silver (Ag) paste or by applying and firing copper (Cu) paste.

In the case of using a copper (Cu) paste, a surface plating process is performed on the copper (Cu) paste layer of the busbar electrode so that the busbar electrode includes a copper (Cu) paste layer and a surface plating layer for soldering. can do.

The plurality of fingerline electrodes are sequentially plated with nickel (Ni) / copper (Cu) / tin (Sn) or nickel (Ni) / copper (Cu) / silver (Ag) from the silicon interface of the solar cell substrate. Can be formed.

In the forming of the busbar electrode, firing of the metal paste may be performed at a temperature condition in the range of 250 ° to 350 °.

According to a solar cell front electrode structure and a method of manufacturing the same, a low cost plating electrode is used in a fingerline region without a subsequent soldering process, and soldering characteristics and a silicon interface are used only in a busbar region in which a ribbon should be soldered. By limiting the use of a metal paste having excellent adhesive properties, the use of expensive silver (Ag) can be reduced, resulting in a reduction in manufacturing cost and high efficiency, and at the same time improving the adhesive properties.

1 is a block diagram of a solar cell according to an embodiment of the present invention.
2 is a flowchart illustrating a method of manufacturing a solar cell front electrode structure according to an embodiment of the present invention.
3A-3D are process cross-sectional views detailing some of the steps of FIG.

Hereinafter, a front electrode structure of a solar cell and a method of manufacturing the same according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

According to the present invention, in order to reduce expensive silver (Ag) usage in a solar cell front electrode structure including a fingerline electrode and a busbar electrode, a fingerline electrode on which a ribbon is not soldered is mainly composed of copper (Cu). The plating electrode is formed of an alloy of nickel (Ni) / copper (Cu) / tin (Sn) or nickel (Ni) / copper (Cu) / silver (Ag).

The fingerline electrode may be formed by sequentially plating nickel (Ni) / copper (Cu) / tin (Sn) or nickel (Ni) / copper (Cu) / silver (Ag) from the silicon interface of the solar cell substrate. have.

In addition, a bus bar electrode requiring relatively strong adhesive strength due to soldering of a ribbon is applied by firing a silver (Ag) paste having excellent adhesion to a silicon interface as compared with a plating electrode. That is, silver (Ag) paste is applied to a region where a busbar electrode on the front electrode layer is to be formed, and then fired to use it as a busbar electrode.

Accordingly, by adopting the plated electrode as the front electrode, it is possible to implement stable adhesion characteristics in consideration of ribbon soldering while reducing the amount of silver (Ag).

1 is a block diagram of a solar cell according to an embodiment of the present invention.

Referring to FIG. 1, a solar cell according to an embodiment of the present invention first includes a solar cell substrate 100 made of silicon. The solar cell substrate 100 may be a crystalline silicon substrate of a first conductivity type. Here, the first conductivity type is p type or n type, and the second conductivity type described later is the opposite conductivity type to the first conductivity type. In the following description, it is assumed that the first conductivity type is p-type and the second conductivity type is n-type.

The surface of the substrate 100 is processed in a concave-convex shape to minimize the reflection of light, and the n-type semiconductor layer 120 of the second conductivity type is formed along the surface of the substrate 100 at a predetermined depth.

Here, the surface of the silicon solar cell substrate 100, that is, the n-type semiconductor layer 120 and the front electrode 110 has a relatively high contact resistance, in one embodiment to improve the contact resistance therebetween In order to form a highly doped emitter (n ++) by locally implanting a high concentration of impurity ions into a region where the front electrode 110 is to be formed in the region of the n-type semiconductor layer 120, a so-called selective emitter emitter) structure can be applied.

In addition, an anti-reflection film 130 is provided on the n-type semiconductor layer 120 to minimize surface reflection.

The front electrode 110 is formed in the electrode region on the anti-reflection film 130 formed on the front surface of the substrate 100.

The front electrode 110 formed on the front surface of the substrate 100 is specifically divided into a finger line electrode 112 and a bus bar electrode 114. The plurality of fingerline electrodes 112 are evenly disposed on the front surface of the solar cell substrate 100 to transfer carriers integrated in the n-type semiconductor layer 120. The busbar electrode 114 is formed in a direction crossing the fingerline electrode 112 on the front surface of the substrate 100 to serve to connect the plurality of fingerline electrodes 112 to each other.

In a subsequent module process of connecting a plurality of solar cells to each other, a ribbon (not shown) is soldered onto the busbar electrode 114 to electrically connect one solar cell with another adjacent solar cell. .

On the other hand, the bottom electrode 140 is formed on the bottom of the back of the substrate 100.

In one embodiment, the rear electrode 140 may be formed by applying an aluminum (Al) paste over the entire rear surface of the substrate 100 and then baking it.

In addition, a p-type back surface field (BSF) 142 is provided inside the substrate 100 in contact with the back electrode 140. The p-type backside field layer 142 serves to induce an electric field on the backside of the substrate 100 to increase the collection rate of the carrier and to improve the photoelectric conversion efficiency.

In the present invention, the busbar electrode 114 includes a metal paste layer, and the plurality of fingerline electrodes 112 are configured to include a plating layer.

Specifically, the busbar electrode 114 includes a metal paste layer mainly composed of silver (Ag) or copper (Cu), which may be formed by applying and firing silver (Ag) or copper (Cu) paste. have.

The plurality of finger line electrodes 112 are formed of a plated electrode including copper (Cu) as a main component. Here, the plating layer constituting the finger line electrode 112 is nickel (Ni) / copper (Cu) / tin (Sn), or nickel (Ni) / copper (Cu) / silver from the silicon interface of the solar cell substrate 100 (Ag) can be formed by plating sequentially.

As such, the fingerline electrode 112 may be formed of a plated electrode including copper (Cu), thereby reducing the amount of silver (Ag), thereby reducing cost and improving efficiency.

Meanwhile, in the case of the busbar electrode 114, adhesion to the surface of the substrate 100, that is, the silicon interface, is more strongly required due to ribbon soldering to be performed subsequently. In addition, the plated electrode has a relatively low adhesion force to the silicon interface compared to the paste electrode using the metal paste, and thus does not satisfy the required degree of adhesion.

Therefore, the busbar electrode 114 is formed of a paste electrode using a metal paste containing silver (Ag) or copper (Cu) as a main component, thereby ensuring a soldering property and a stable adhesive force against ribbon bonding. In this case, the bus bar electrode 114 may be formed by applying a metal paste of silver (Ag) or copper (Cu) by a screen printing process and then firing at an appropriate temperature.

However, since copper (Cu) cannot be ribbon soldered, when the bus bar electrode 114 is formed using a copper (Cu) paste, a surface plating process using copper (Sn) or silver (Ag) is additionally performed. It is preferable to proceed so that a ribbon soldering is possible. In this case, the busbar electrode 114 further includes a copper (Cu) paste layer on the entire surface of the substrate 100 and a surface plating layer on the copper (Cu) paste layer configured to include tin (Sn) or silver (Ag). do.

The metal paste is a mixture of metal powders of silver (Ag) or copper (Cu), glass frit, organics, solvents, and materials such as nonvolatile polymers and rosin. At least about 70% by weight of the metal paste constituting 114 is composed of silver (Ag) or copper (Cu).

As such, the finger line electrode 112, which occupies the largest area in the front electrode 110, is formed as a plating electrode including a plating layer, thereby reducing the amount of silver (Ag) and a bus bar electrode requiring a relatively high adhesive strength property. The 114 may be formed of a paste electrode including a metal paste layer, thereby simultaneously implementing cost reduction, efficiency improvement, and stable adhesive force characteristics.

2 is a flowchart illustrating a method of manufacturing a solar cell front electrode structure according to an embodiment of the present invention.

As shown in FIG. 2, first, a texturing process is performed to form irregularities on the surface of the solar cell substrate 100 (S110). Here, the solar cell substrate 100 may be a crystalline silicon substrate of a first conductivity type. The first conductivity type is p type or n type, and the second conductivity type described later is the opposite conductivity type to the first conductivity type. In the following description, it is assumed that the first conductivity type is p-type and the second conductivity type is n-type.

The texturing process is to reduce light reflection on the surface of the substrate 100 and may be performed using a dry etching method such as a wet etching method or a reactive ion etching method.

In this state, the n-type semiconductor layer 120 is formed by performing a diffusion process (S120). Specifically, the solar cell substrate 100 is provided in the chamber, and the phosphorus (P) ions are diffused by supplying a gas (for example, POCl ₃ ) containing a second conductivity type impurity ion, that is, an n-type impurity ion. do. As a result, the n-type semiconductor layer 120 having a predetermined depth is formed on the upper layer of the substrate 301.

In the diffusion process, a phosphor-silicate glass (PSG) film is formed on the surface of the substrate 100 by reacting phosphorus (P) ions with silicon (Si) of the solar cell substrate 100, thereby removing the same through etching.

Subsequently, the anti-reflection film 130 is deposited on the entire surface of the substrate 100, and a portion of the n-type semiconductor layer 120 is exposed by removing a portion of the area on the anti-reflection film 130 using a laser, thereby exposing the fingerline electrode. An electrode region in which the 112 is to be formed is patterned (S130). Here, the anti-reflection film 130 may be a silicon nitride film (SiN _x ).

Then, by applying a aluminum (Al) paste for forming the back electrode 140 on the back of the substrate 100 by screen printing process and firing, the back having a predetermined thickness on the entire surface of the back of the substrate 100 An electrode 140 is formed (S150). At this time, the back electrode 140 is formed by the firing process, and the back field layer 142 is formed inside the back of the substrate 100.

As described above, in the state where the solar cell substrate 100 is prepared, the plurality of fingerline electrodes 112 including the plating layer on the patterned electrode region on the front surface of the solar cell substrate 100 on which the anti-reflection film 130 is formed through the plating process. To form (S160).

In one embodiment, the plurality of fingerline electrodes 112 are formed of a plated electrode containing copper (Cu) as a main component.

Since copper (Cu) has poor plating characteristics on the silicon substrate 100, in consideration of the advantages, copper (Cu) is first plated with nickel (Ni) in the finger line region of the substrate 100, and then the copper plating process is performed. You can proceed. Further, when tin (Sn) or silver (Ag) is plated thinly on the surface of copper (Cu), soldering properties with a ribbon can be improved.

That is, the plurality of finger line electrodes 112 are nickel (Ni) / copper (Cu) / tin (Sn), or nickel (Ni) / copper (Cu) / silver (Ag) from the silicon interface of the solar cell substrate 100. ) Can be formed by plating sequentially, thereby improving the soldering and adhesion properties.

After the formation of the fingerline electrode 112 is completed as described above, a screen printing process is performed to form the metal paste for forming the busbar electrode 114 on the entire surface of the substrate 100 on which the plurality of fingerline electrodes 112 are formed. To apply (S170).

Thereafter, when the firing process is performed, the formation of the busbar electrode 114 including the metal paste layer connecting the plurality of fingerline electrodes 112 to each other is completed (S170).

In this case, the bus bar electrode 114 may be formed by applying and firing silver (Ag) paste or by applying and firing copper (Cu) paste.

However, since copper (Cu) cannot be soldered with a ribbon, tin (Sn) or silver (Ag) on a copper (Cu) paste layer forming the busbar electrode 114 when using a copper (Cu) paste. ), The busbar electrode 114 may be formed to include a copper (Cu) paste layer and a surface plating layer for soldering.

In the case of the metal paste, it is usually based on high-temperature firing of about 900 °, but such a temperature condition cannot be applied using a plating electrode as in the present invention.

That is, in the present invention, since the coating and firing of the metal paste for forming the busbar electrode 114 on the fingerline electrode 112 is performed while the fingerline electrode 112 is formed as the plating electrode, the previously formed plating electrode is formed. Low temperature firing processes that do not affect the system should be applied.

Therefore, in the present invention, it is preferable to use a low-temperature metal paste for forming the busbar electrode 114, and to proceed with the firing process by applying a temperature condition of about 300 °, specifically, 250 ° to 350 °. Do. As a result, it is expected to maintain the adhesive force of the busbar electrode 114 using the metal paste and to improve the soldering characteristics while minimizing the influence on the previously formed plating electrode.

3A to 3D are cross-sectional views illustrating some steps of FIG. 2 in detail, illustrating a process of forming a fingerline electrode 112 including nickel (Ni), copper (Cu), and tin (Sn).

First, as shown in FIG. 3A, a solar cell substrate 100 of silicon material for preparing a front electrode structure is prepared.

Here, the solar cell substrate 100 may be a p-type crystalline silicon substrate of a first conductivity type, and the rear electric field layer 142 and the rear electrode 140 may be previously provided on the rear surface of the solar cell substrate 100. .

In addition, an n-type semiconductor layer 120 having a predetermined depth and a partial region for forming the fingerline electrode 112 are exposed on the front surface of the solar cell substrate 100. 130 may be provided in advance. In this case, the exposed region is a region where plating is performed to form the fingerline electrode 112, and a position thereof corresponds to the highly doped region n ++ of the n-type semiconductor layer 120.

As described above, in the state where the solar cell substrate 100 is prepared, nickel (Ni) plating of FIG. 3B, copper (Cu) plating of FIG. 3C, and tin (Sn) plating of FIG. 3D are sequentially performed to obtain nickel (Ni) / The fingerline electrode 112 made of the plating layers 112a, 112b, and 112c including copper (Cu) and tin (Sn) may be formed.

The structure of the front electrode structure of the solar cell and the manufacturing method thereof according to the present invention are not limited to the above-described embodiments, and may be variously modified within the range allowed by the technical idea of the present invention.

100: substrate
110: front electrode
112: fingerline electrode
114: busbar electrode
120: semiconductor layer
130: antireflection film
140: rear electrode
142: rear layer

Claims (11)

delete delete delete delete delete Preparing a solar cell substrate;
Forming a plurality of fingerline electrodes including a plating layer on a front surface of the solar cell substrate through a plating process; And
Forming a busbar electrode including a metal paste layer connecting the plurality of fingerline electrodes to each other by applying and firing a metal paste for forming a busbar electrode on a front surface of the substrate on which the plurality of fingerline electrodes are formed; Method for manufacturing a solar cell front electrode structure comprising a.
The method of claim 6, wherein the metal paste layer of the bus bar electrode,
A method of manufacturing a solar cell front electrode structure, which is formed by applying and firing silver (Ag) paste.
The method of claim 6, wherein the metal paste layer of the bus bar electrode,
A method of manufacturing a solar cell front electrode structure, which is formed by coating and firing a copper (Cu) paste.
9. The method of claim 8,
Surface plating treatment is performed on the copper (Cu) paste layer of the busbar electrode, so that the busbar electrode includes a copper (Cu) paste layer and a surface plating layer for soldering. Manufacturing method.
The method of claim 6, wherein the plating layer of the plurality of finger line electrodes,
The solar cell substrate is formed by sequentially plating nickel (Ni) / copper (Cu) / tin (Sn) or nickel (Ni) / copper (Cu) / silver (Ag) from the silicon interface of the solar cell substrate. Method for manufacturing a battery front electrode structure.
The method of claim 6, wherein in the forming of the busbar electrode,
Firing of the metal paste is a method of manufacturing a solar cell front electrode structure, characterized in that the temperature is performed in the range of 250 ° to 350 °.

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