KR101305055B1 - Backside electrode part for solar cell and method for preparing the same - Google Patents

Abstract

The present invention relates to a solar cell back electrode unit and a solar cell including the same, a method for manufacturing the solar cell, the rear electrode unit and the solar cell, according to the present invention, increases the moving speed and moving distance of the electrons in the solar cell and the minority carrier recombination By reducing the photoelectron conversion efficiency can be increased to manufacture a highly efficient solar cell.

Solar cell, back electrode, back layer, double thin film

Description

Back electrode part for solar cell and manufacturing method thereof {BACKSIDE ELECTRODE PART FOR SOLAR CELL AND METHOD FOR PREPARING THE SAME}

The present invention relates to a solar cell back electrode unit and a solar cell comprising the same, the rear electrode unit and a method of manufacturing a solar cell comprising the same.

The main direction of technological development of solar cell, which is the representative alternative energy of the future, is high efficiency, high purity, integration, and productivity improvement. Above all, the most demanding of solar power generation facilities is the conversion efficiency of solar cells. The conversion efficiency of single crystal solar cells currently used for each household is about 15%, and other energy such as thermal power generation is required. This is because the conversion efficiency of the power generation equipment by P is significantly inferior to about 45%.

Therefore, since the development of silicon single crystal solar cells, researches for increasing the efficiency of solar cells such as a back surface field type (BSF), violet cell, and anti-reflective cell (CNR) have continued. In recent years, efforts have been made to develop high efficiency solar cells with conversion efficiency of 20% or more, such as solar cell efficiency by surface plasmon excitation, ultra-high efficiency compound semiconductor multi-junction solar cell, solar cell and thermoelectric device. Reached.

A general solar cell manufacturing process involves a high temperature process of 400 to 1100 ° C., and in particular, a rear electrode part forming process basically includes a heat treatment process. In this case, when the back electrode portion forming process is performed at the beginning and the middle of the entire solar cell manufacturing process, heat load is applied to the back electrode portion. As a result, a back electrode material made of metal such as copper, nickel, iron, and silver, Alternatively, impurities contained in the substrate diffuse into the silicon layer, which forms a place where the excited carriers can recombine, which in turn causes a problem of degrading the performance of the solar cell.

Therefore, the single deposition and continuous heating process of the existing Al thin film (1000 nm), despite the advantages of using Al as the back electrode, opens voltage due to the acceleration of electron-hole recombination due to the back bonding occurring during the heat treatment. The short-circuit current density is lowered and its utility is lowered.

In addition, the paper [IEEE Trans. Elec. Device, 24, 337, 1979 and Semicond. Sci. Technol. 15 , 322, 2000] attempted to solve the problem by finding an optimized condition by reducing the reflectance or changing the heat treatment conditions of the rear electrode by making an uneven structure on the n-emitter surface of the pn junction silicon matrix. As a result, there is no significant increase in battery efficiency, and there is an urgent need for an effective method for manufacturing a solar cell rear electrode part having high conversion efficiency.

Accordingly, the present invention is to solve the above problems, comprising a rear field layer formed between the semiconductor layer and the rear electrode of the solar cell to reduce the recombination of minority carriers occurring on the surface of the junction portion to increase the conversion efficiency It is an object of the present invention to provide a high efficiency solar cell by increasing the photoelectric conversion efficiency of a solar cell by providing a back electrode portion and a method of manufacturing the same.

In order to achieve the above object, one aspect of the present invention is a manufacturing method of a solar cell rear electrode including a semiconductor layer, a front electrode and a rear electrode, a double metal thin film formed on the back of the semiconductor layer Provided is a manufacturing method of a solar cell rear electrode unit.

In one embodiment of the present invention, the method of manufacturing the solar cell back electrode portion includes the following steps:

Forming a primary metal thin film on a back surface of the semiconductor layer;

Forming a back surface field (BSF) layer by rapid thermal annealing (RTA) of the semiconductor layer on which the primary metal thin film is formed; And

Forming a rear electrode by forming a secondary metal thin film on the rapid heat-treated primary metal thin film.

In another embodiment of the present invention, the primary metal thin film may be one or more metals selected from the group consisting of Al, B, Ga, In and Tl.

In another embodiment of the present invention, the secondary metal thin film may be one or more metals selected from the group consisting of Cu, W, Fe, Al, C, Ni and Ti.

Another aspect of the present invention provides a solar cell rear electrode part including a semiconductor layer, a front electrode part and a rear electrode part, and including a metal thin film formed on a rear surface of the semiconductor layer.

In one embodiment of the present invention, the solar cell rear electrode part includes a back surface field layer formed by forming a first metal thin film on the back surface of the semiconductor layer and rapidly heat-treating and a second metal thin film formed on the back surface layer. An electrode.

Another aspect of the present invention provides a solar cell and a method for manufacturing the same, including a rear electrode part manufactured according to the method of manufacturing the solar cell rear electrode part.

According to the present invention, a method of manufacturing the solar cell rear electrode part is an easy method including a process of forming a metal thin film forming the rear electrode part and a rapid heat treatment step, and by the method of manufacturing the solar cell rear electrode part. In addition, by increasing the moving speed and moving distance of electrons in the solar cell and reducing the minority carrier recombination, the photoelectric conversion efficiency of the solar cell can be increased to manufacture a highly efficient solar cell.

In addition, the present invention does not require additional equipment investment because it utilizes 100% of the equipment established in the existing, it can be said to be a method that meets the low power unit cost, which is one of the important challenges in the solar cell field, the solar cell is currently in a stale state Since the present invention can be easily applied to improve efficiency, various applications to photoelectric conversion materials used in low-cost, high-efficiency solar cells are possible.

One aspect of the present invention, in a solar cell comprising a semiconductor layer, a front electrode portion and a back electrode portion, comprising forming a double metal thin film forming a back electrode portion on the back of the semiconductor layer, solar cell back electrode Provided is a method for producing a part.

In one embodiment of the present invention, the method of manufacturing the solar cell back electrode portion includes the following steps:

Forming a primary metal thin film on a back surface of the semiconductor layer;

Forming a back surface field (BSF) layer by rapid thermal annealing (RTA) of the semiconductor layer on which the primary metal thin film is formed; And

Forming a rear electrode by forming a secondary metal thin film on the rapid heat-treated primary metal thin film.

In another embodiment of the present invention, the primary metal thin film may be one or more metals selected from the group consisting of Al, B, Ga, In and Tl.

In another embodiment of the present invention, the secondary metal thin film may include at least one metal selected from the group consisting of Cu, W, Fe, Al, C, Ni and Ti.

As used herein, the terms “front side” and “back side” refer to surfaces on which a front electrode portion and a back electrode portion are formed in a semiconductor layer which is an active layer of a solar cell, respectively.

In another embodiment of the present invention, the semiconductor layer may be a p-n junction semiconductor layer, for example, may be a p-n junction semiconductor layer including a p-n junction silicon layer, a III-V group compound semiconductor layer. For example, a p-n junction silicon layer may be used as the semiconductor layer, wherein the silicon may be crystalline, polycrystalline, or amorphous silicon, but is not limited thereto.

For example, the pn junction silicon layer is a p-type silicon layer doped with group III elements, such as B, Ga, and In, and an n-type already doped with group 5 elements, such as P, As, and Sb, for example. The ground layer is formed by bonding. However, the p-n junction semiconductor layer of the present invention is not limited thereto.

In another embodiment of the present invention, the primary metal thin film forming the rear electrode portion may include at least one metal selected from the group consisting of Al, B, Ga, In and Tl. For example, the primary metal thin film may include Al. The secondary metal thin film may include at least one metal selected from the group consisting of Cu, W, Fe, Al, C, Ni, and Ti. For example, the secondary metal thin film may include Al.

In another embodiment of the present invention, the primary metal thin film and the secondary metal thin film may include different metals or the same metal. For example, the primary metal thin film and the secondary metal thin film may include Al.

 The method of forming the primary metal thin film and the secondary metal thin film is not particularly limited, but may be formed by sputtering, thermal image deposition, screen printing, or the like.

In another embodiment of the present invention, in consideration of the formation of the efficient rear field layer and the light conversion rate, and the type of metal forming the back electrode portion, including the primary metal thin film and the secondary metal thin film The rear electrode portion may have a thickness of about 0.5 to 10 μm, preferably about 1 to about 5 μm, more preferably about 1 to about 3 μm, but is not limited thereto. For example, the thickness of the primary metal thin film is about 500 nm, the thickness of the secondary metal thin film is about 500 nm, and the total thickness after forming the primary and secondary metal thin films may be about 1 μm.

In another embodiment of the present invention, the temperature of the rapid heat treatment process of the primary metal thin film for forming the back surface field layer may be appropriately selected according to the type of metal, specifically, the melting point of the metal used Can be processed at nearby temperatures. Specifically, the temperature of the rapid heat treatment process may be a temperature of ± 10% of the melting point of the metal used. For example, when the primary metal thin film includes Al, the temperature of the rapid heat treatment process may be 700 ° C. or higher, for example, 700 ° C. to 850 ° C., but is not limited thereto. The rapid heat treatment time may be, for example, 60 seconds or less, but is not limited thereto.

Another aspect of the present invention provides a solar cell rear electrode part including a semiconductor layer, a front electrode part and a rear electrode part, and including a metal thin film formed on a rear surface of the semiconductor layer.

In the embodiment of the present invention, the solar cell rear electrode part is formed on the rear surface of the semiconductor layer by forming a primary metal thin film and rapidly heat-treating the secondary electric field formed on the primary metal thin film and the rapid heat treatment It may include a back electrode including a metal thin film.

Another aspect of the present invention provides a solar cell and a method of manufacturing the solar cell comprising a back electrode manufactured by the method for manufacturing a solar cell rear electrode.

In the embodiment of the present invention, the method of manufacturing the solar cell includes the following steps:

Preparing the semiconductor layer:

Forming a front electrode part on the entire surface of the semiconductor layer;

Forming a rear electrode part on a rear surface of the semiconductor layer on which the front electrode part is formed, by the manufacturing method of the rear electrode part according to the present invention.

In addition, it is apparent to those skilled in the art that the semiconductor layer of the solar cell and other structures and materials, and a method of forming the same are all applicable to those skilled in the art.

1 is a flowchart of a method of manufacturing a solar cell back electrode unit according to an embodiment of the present invention, Figure 2 is a schematic diagram of a method of manufacturing a solar cell back electrode unit according to an embodiment of the present invention. Hereinafter, the present invention will be described in more detail with reference to FIGS. 1 and 2. However, the present invention is not limited to the contents described herein but may be embodied in other forms.

(1) forming a metal thin film on the back surface of the semiconductor layer (S10)

As shown in FIG. 2 (a), in the method for manufacturing a solar cell rear electrode part of the present invention, a primary metal thin film 10 is formed on a rear surface of a prepared semiconductor layer.

For example, the semiconductor layer may be a p-n junction semiconductor layer, and may be, for example, a p-n junction semiconductor layer including a p-n junction silicon layer, a III-V compound semiconductor layer, or the like. For example, a p-n junction silicon layer may be used as the semiconductor layer, wherein the silicon may be crystalline, polycrystalline, or amorphous silicon, but is not limited thereto.

For example, the pn junction silicon layer is a p-type silicon layer doped with group III elements, such as B, Ga, and In, and an n-type already doped with group 5 elements, such as P, As, and Sb, for example. The ground layer is formed by bonding. However, the p-n junction semiconductor layer of the present invention is not limited thereto.

For example, the primary metal thin film forming the rear electrode part may include one or more metals selected from the group consisting of Al, B, Ga, In, and Tl. For example, the primary metal thin film may include Al.

remind The method of forming the primary metal thin film is not particularly limited, but may be formed by, for example, sputtering, thermo-deposition, screen printing, or the like.

(2) forming a back field layer by rapid thermal treatment on the substrate on which the primary Al metal thin film is formed (S20)

As shown in FIG. 2 (b), the back surface field layer 20 is formed by rapid heat treatment of the substrate on which the primary metal thin film is formed.

The temperature of the rapid heat treatment process of the primary metal thin film for forming the backside field layer may be appropriately selected according to the type of metal, and specifically, may be processed at a temperature near the melting point of the metal to be used. For example, when the primary metal thin film includes Al, the temperature of the rapid heat treatment process may be 700 ° C. or higher, for example, 700 ° C. to 850 ° C., but is not limited thereto. The rapid heat treatment time may be, for example, 60 seconds or less, but is not limited thereto. The rapid heat treatment may use rapid thermal annealing (RTA) equipment, but is not limited thereto.

(3) forming a rear electrode by forming a secondary metal thin film on the rear electric field layer (S30)

As shown in FIG. 2 (c), a rear electrode is formed by forming a secondary metal thin film 30 on the rapid heat-treated primary metal thin film.

The secondary metal thin film may include at least one metal selected from the group consisting of Cu, W, Fe, Al, C, Ni, and Ti. Preferably, the primary metal thin film may include Al.

The secondary metal thin film on the back surface field layer is not limited to a specific method, and may be formed by, for example, sputtering, thermal image deposition, screen printing, or the like.

Here, the thickness of the rear electrode part including the primary metal thin film and the secondary metal thin film is about 0.5 to 10 μm in consideration of the efficient formation of the rear electric field layer, the light conversion rate, and the type of metal forming the rear electrode part. It may be, but preferably, about 1 to about 5 μm, more preferably about 1 to about 3 μm, but is not limited thereto. For example, the thickness of the primary metal thin film is about 500 nm, the thickness of the secondary metal thin film is about 500 nm, and the total thickness after forming the primary and secondary metal thin films may be about 1 μm.

As described above, the metal layer included in the rear electrode part according to the present invention is formed by forming the rear electrode layer and the rear electrode, respectively, so that the rear side at the time of manufacture compared to the rear electrode part formed by conventional single deposition and heat treatment. Since no heat load is applied to the electrode, conversion efficiency can be increased by reducing the recombination of minority carriers generated at the surface of the junction between the semiconductor layer and the back electrode.

Hereinafter, the present invention will be described in more detail with reference to Examples.

      [Example]

Example 1

As shown in Fig. 2A, using a pn junction single crystal silicon substrate as a semiconductor layer, a Ti 50 nm / Ag 100 nm layer is formed on the front surface thereof as a front electrode, remind The primary Al metal thin film 10 was formed on the back side of the pn junction single crystal silicon substrate using a sputter deposition machine. At this time, the thickness of the primary Al metal thin film was deposited to 200 nm. Subsequently, as shown in FIG. 2B, the pn junction single crystal silicon substrate on which the primary Al metal thin film was formed was subjected to rapid heat treatment at 850 ° C. for 30 seconds using an RTA apparatus. By the above process, the backside field layer 20 is formed at the junction of the primary Al metal thin film and the semiconductor layer. Subsequently, as shown in FIG. 2C, a secondary Al metal thin film was deposited to a thickness of 800 nm using a sputter evaporator on the rapidly heat-treated primary metal thin film formed on the pn junction silicon semiconductor layer to form a rear electrode. In this embodiment, the total thickness of the rear electrode part was 1 μm.

In the silicon solar cell including the back electrode part including the first and second Al metal thin films formed in a double layer (two step process) according to the above embodiment, the Al metal thin film is subjected to a single step (one step process: comparative example). Compared to the silicon solar cell including the back electrode manufactured by forming the photoelectric conversion efficiency, etc. [Voc = open-circuit voltage, Jsc = short-circuit current, FF = fill factor ), EFF = efficiency (Table 1 and Figure 3).

[Table 1]

Example  2

In the same manner as in Example 1, except that the total thickness of the rear electrode part including the primary Al metal film and the secondary Al metal film was 2 μm.

According to the embodiment, a silicon solar cell including a back electrode part including a first and a second Al metal thin film formed by a double, a silicon solar cell including a back electrode part manufactured by forming an Al metal thin film by a single process ( Compared with Comparative Example), improved photoelectric conversion efficiency was shown (Table 2, FIG. 4 and FIG. 5).

[Table 2]

As mentioned above, the present invention has been described in detail by way of example, but the present invention is not limited to the above embodiments, and may be modified in various forms, and having ordinary skill in the art within the technical idea of the present invention. It is apparent that many other variations are possible by one.

       1 is a flowchart of a method of manufacturing a back electrode unit for a solar cell according to an embodiment of the present invention.

2 is a schematic diagram of a method for manufacturing a back electrode unit for a solar cell according to an embodiment of the present invention.

3 is a graph showing the light conversion efficiency rate of the solar cell according to Example 1 of the present invention.

4 is a graph showing the light conversion efficiency rate of the solar cell according to the second embodiment of the present invention.

FIG. 5 is a SEM photograph showing a cross section of a solar cell rear electrode unit according to Embodiment 2 of the present invention. FIG.

Description of the Related Art [0002]

10: Primary Al metal thin film for forming backside field layer

20: backside field layer formed by rapid heat treatment process

30: secondary Al metal thin film for forming the rear electrode

Claims (9)

A manufacturing method of a solar cell rear electrode part comprising a semiconductor layer, a front electrode part and a rear electrode part, Forming a primary metal thin film on a back surface of the semiconductor layer; Forming a back surface field (BSF) layer by performing rapid thermal annealing (RTA) on the semiconductor layer on which the primary metal thin film is formed for more than 0 seconds to 60 seconds; And Forming a rear electrode part by forming a secondary metal thin film on the rapid heat-treated primary metal thin film, The thickness of the rear electrode portion including the primary metal thin film and the secondary metal thin film is 1 μm to 3 μm, Method for manufacturing a back electrode portion for a solar cell. The method of claim 1, The primary metal thin film is one of Al, B, Ga, In and Tl that comprises at least one metal selected from the group consisting of, a solar cell back electrode portion manufacturing method. The method of claim 1, The secondary metal thin film comprises at least one metal selected from the group consisting of Cu, W, Fe, Al, C, Ni and Ti, solar cell manufacturing method of the back electrode portion. The method of claim 1, The semiconductor layer is a p-n junction semiconductor layer, the manufacturing method of the solar cell back electrode portion. 5. The method of claim 4, The pn junction semiconductor layer is monocrystalline, polycrystalline, or amorphous The manufacturing method of the back electrode part for solar cells which is a pn junction silicon layer. The method of claim 1, The primary metal thin film and the secondary metal thin film will include Al, the manufacturing method of the solar cell back electrode. delete The method of claim 1, The temperature of the rapid heat treatment process for forming the back surface field layer is near the melting point of the metal forming the primary metal thin film, the manufacturing method of the back electrode portion for a solar cell. A method of manufacturing a solar cell including a semiconductor layer, a front electrode portion, and a back electrode portion, The manufacturing method of the solar cell containing manufacturing the said back electrode part by the manufacturing method in any one of Claims 1-6.

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