KR20090065894A - Tandem structure cigs solar cell and method for manufacturing the same - Google Patents

Abstract

A CIGS(Copper Indium Gallium Selenide) solar cell of a tandem structure and a manufacturing method thereof are provided to lower an energy barrier at a boundary between two cells by introducing metallic nano-particles into the boundary. A CIGS solar cell of a tandem structure is formed by stacking a lower CIGS solar cell(210) and an upper solar cell(220). The lower CIGS solar cell and the upper solar cell are stacked sequentially. A nano-particle layer including metallic nano-particles is formed at a boundary between the lower CIGS solar cell and the upper CIGS solar cell. The metallic nano-particles included in the nano-particle layer are formed with at least one of Au, Ag, and Ni. The CIGS solar cells include a CIGS layer, a buffer layer, and a ZnO layer.

Description

Tandem structured CIS solar cell and its manufacturing method {TANDEM STRUCTURE CIGS SOLAR CELL AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a tandem structure CIGS solar cell and a method of manufacturing the same. More specifically, by forming a metal nanoparticle layer between two CIGS solar cells included in a tandem CIGS solar cell to lower the energy barrier at the cell interface, the tunneling movement of electrons and holes is freed. It relates to a tandem structure CIGS solar cell and a method of manufacturing the same to increase the efficiency.

Recent rising oil prices, global environmental problems, depletion of fossil energy, waste disposal of nuclear power generation, and the selection of locations due to the construction of new power plants are raising interest in new and renewable energy. Research and development on batteries is being actively conducted.

A solar cell is a device that converts light energy into electrical energy by using a photovoltaic effect. The solar cell is classified into a silicon solar cell, a thin film solar cell, a dye-sensitized solar cell, and an organic polymer solar cell. . These solar cells are used independently as main power sources such as electronic clocks, radios, unmanned light towers, satellites, rockets, etc., and are also used as auxiliary power sources in connection with commercial AC power systems. Increasingly, interest in solar cells is increasing.

In such solar cells, it is very important to increase the conversion efficiency related to the ratio of converting incident sunlight into electrical energy. Various studies have been conducted to increase the conversion efficiency, and the development of a technology for increasing the conversion efficiency by actively incorporating a thin film having a high light absorption coefficient into the solar cell has been actively conducted.

CIGS (Copper Indium Galium Selenide) was introduced as a material having a high light absorption coefficient, and it was found that high conversion efficiency can be obtained by using such CIGS in the manufacture of thin film solar cells. Accordingly, film-type CIGS solar cells are spotlighted as high efficiency alternative energy sources.

1 shows the structure of a conventional single cell CIGS solar cell. As shown in FIG. 1, the conventional CIGS solar cell 100 includes a glass substrate 110, a molybdenum (Mo) film 120, a CIGS film 130, a cadmium sulfide (CdS) film 140, and i. A zinc oxide (i-ZnO) film 150, a doped Zno: Al film 160, and an antireflection film 170 are stacked in this order, and a grid electrode 180 is formed thereon.

The CIGS film 130 of the single cell CIGS solar cell 100 is p-type and the i-ZnO film 150 is n-type. In this case, the difference in energy band gap and lattice constant between the CIGS film 130 and the i-ZnO film 150 is relatively large, which may reduce the efficiency of the solar cell. To prevent this, a cadmium sulfide (CdS) film as a buffer layer ( 140 is introduced between the CIGS film 130 and the i-ZnO film 150. The cadmium sulfide (CdS) film 140 increases the efficiency of the solar cell by alleviating the difference in energy band gap and lattice constant between the CIGS film 130 and the i-ZnO film 150.

Meanwhile, in order to further increase the efficiency of CIGS solar cells, two single-cell CIGS solar cells were stacked and used. The structure of a CIGS solar cell formed by stacking two cells is called a tandem structure.

However, such a tandem structure CIGS solar cell has a p-n structure or an n-p structure in both the lower cell and the upper cell, so that n-p junctions or p-n junctions are formed at the interface, and thus have different electrical directions. As a result, an energy barrier is formed very high at the interface between the two cells, thereby inhibiting the mobility of electrons and holes. Accordingly, there is a problem that can not maximize the efficiency of the solar cell even by the tandem structure.

Therefore, in the tandem structured CIGS solar cell, it is necessary to develop a technology for maximizing the efficiency of the solar cell by improving the mobility of electrons and holes at the interface between two cells.

The present invention is to solve the above problems, in the tandem structure CIGS solar cell tandem structure CIGS solar cell is maximized by lowering the energy barrier at the interface between the two cells to improve the mobility of electrons and holes (hole) To provide that purpose.

It is another object of the present invention to reduce the energy barrier by introducing metal nanoparticles at the interface between two cells of a tandem-structured CIGS solar cell, thereby facilitating the tunneling movement of electrons and holes. It is to provide a method for producing a CIGS solar cell.

According to an embodiment of the present invention for achieving the above object, in the tandem structure CIGS solar cell formed by stacking the lower CIGS solar cell and the upper CIGS solar cell in order, the lower CIGS solar cell And a tandem structured CIGS solar cell, comprising a nanoparticle layer composed of metal nanoparticles at an interface of an upper CIGS solar cell.

The tandem structured solar cell of the present invention is not necessarily limited to the above structure, and a plurality of dual solar cells further including a double solar cell in which a lower CIGS solar cell and an upper CIGS solar cell are sequentially stacked. It may be provided.

The material of the metal nanoparticles included in the nanoparticle layer may be at least one of gold (Au), silver (Ag), and nickel (Ni).

The CIGS solar cells may each include a CIGS film, a buffer layer, and a zinc oxide (ZnO) film that are sequentially stacked, and the CIGS film included in the upper CIGS solar cell is larger than the CIGS film included in the lower CIGS solar cell. It may have an energy band gap.

The CIGS solar cells may include a zinc oxide (ZnO) film, a buffer layer, and a zinc oxide (ZnO) film that are sequentially stacked, and the CIGS film included in the lower CIGS solar cell is included in the upper CIGS solar cell. It may have a larger energy band gap than the CIGS film.

The buffer layer may be one of a cadmium sulfide (CdS) film, a zinc sulfide (ZnS) film, and an indium oxide (In ₂ O ₃ ) film.

According to another embodiment of the present invention for achieving the above object, in the manufacturing method of a tandem structure CIGS solar cell formed by stacking the lower CIGS solar cell and the upper CIGS solar cell in order, the lower CIGS Stacking a solar cell, forming a nanoparticle layer composed of metal nanoparticles on the lower CIGS solar cell, and laminating the upper CIGS solar cell on the nanoparticle layer Provided is a method for producing a tandem structured CIGS solar cell.

The material of the metal nanoparticles included in the nanoparticle layer may be at least one of gold (Au), silver (Ag), and nickel (Ni).

Forming the nanoparticle layer may include applying a colloidal solution containing the metal nanoparticles.

The forming of the nanoparticle layer may include depositing a metal thin film, and forming the metal nanoparticle by heat treating the metal thin film.

The stacking of the bottom CIGS solar cell and the stacking of the top CIGS solar cell may include stacking a CIGS film, a buffer layer, and a zinc oxide (ZnO) film in sequence.

The stacking of the bottom CIGS solar cell and the stacking of the top CIGS solar cell may include stacking a zinc oxide (ZnO) film, a buffer layer, and a CIGS film in sequence.

The buffer layer may be one of a cadmium sulfide (CdS) film, a zinc sulfide (ZnS) film, and an indium oxide (In ₂ O ₃ ) film.

According to the present invention, in the tandem structured CIGS solar cell, by introducing metal nanoparticles at the interface between two cells, the energy barrier at the interface can be lowered to free the tunneling movement of electrons and holes, thereby improving efficiency. Maximized tandem structure CIGS solar cell can be obtained.

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

2 is a cross-sectional view showing the configuration of a CIGS solar cell according to an embodiment of the present invention.

As shown in FIG. 2, in the CIGS solar cell 200 of the present invention, a nanoparticle layer 230 is introduced between two cells of a substrate tandem structure CIGS solar cell. It features.

To increase the efficiency of CIGS solar cells, tandem structured CIGS solar cells, which mechanically or integrally stack two cells, are widely used, and tandem structured CIGS solar cells are divided into substrate type and superstrate type. .

The substrate tandem structure is a laminate of a single cell CIGS solar cell formed by depositing a CdS film as a buffer layer and a ZnO film as a window layer for absorbing sunlight on the CIGS film, and the super tandem structure is a substrate type. On the contrary, a single cell CIGS solar cell formed by first depositing a ZnO film as a window layer and then depositing a CdS film and a CIGS film as a buffer layer thereon is stacked.

FIG. 2 is a substrate type tandem structure CIGS solar cell among the tandem structures, and a CdS film 214 and 224 film and an i-ZnO film on the substrate type CIGS solar cell, that is, CIGS film 212 and 222. In the case where two single cell solar cells in which 215 and 225 are sequentially deposited are stacked, a nanoparticle layer 230 is introduced between the two cells.

In a typical tandem solar cell, two cells, that is, the lower cell and the upper cell, have different directions between their interfaces. Referring to the CIGS solar cell 200 of FIG. 2, both the lower cell 210 and the upper cell 220 have a p-n junction structure in an upward direction. In this case, since the n-p junction is formed at the interface between the lower cell 210 and the upper cell 220, the movement of electrons and holes can be inhibited due to the energy barrier generated at this time. For this reason, even if a CIGS solar cell is manufactured with a tandem structure, sufficient efficiency will not be obtained.

The CIGS solar cell 200 of the present invention minimizes the generation and diffusion of a depletion layer in which the nanoparticle layer 230 between the lower cell 210 and the upper cell 220 causes an increase in the energy barrier at the interface.

Specifically, since the ZnO: Al film 216 of the lower cell 210 shows high n-type doping and the CIGS film 223 of the upper cell 220 shows high p-type doping, the lower cell 210 A high concentration of doped p + -n + junction occurs at the interface between the and upper cell 220, and the movement of electrons and holes can be inhibited by the high energy barrier created by the reasons described above, The nanoparticle layer 230 composed of the metal particles minimizes the generation of a depletion layer in the bonding with the semiconductor. Accordingly, the thinner the energy barrier, the easier the tunneling movement of the electrons and holes forming a high concentration of p + -n + junction.

As described above, the nanoparticle layer 230 should be a material capable of minimizing depletion layer generation. Since the smaller the area to be bonded to the semiconductor can minimize the generation of depletion layer, it is desirable to minimize the size of the particles included in the nanoparticle layer 230, and quantitatively the size of the particles to several tens of nanometers or less It is desirable to. As the metal nanoparticles included in the nanoparticle layer 230, gold (Au), silver (Ag), nickel (Ni), or the like may be used. In addition, the density of the nanoparticle layer 230 may be appropriately selected within a range that does not prevent the passage of sunlight from the upper cell 220 to the lower cell 210 while minimizing the depletion layer generation as described above. have.

3 is a cross-sectional view showing the configuration of a CIGS solar cell according to another embodiment of the present invention.

The CIGS solar cell 300 of FIG. 3 is a super-tandem tandem structure CIGS solar cell in which a nanoparticle layer 330 is introduced between two cells, such as the CIGS solar cell 200 of FIG. 2. It is characterized by.

The CIGS solar cell 300 has a super straight tandem structure in which CdS films 314 and 324 and CIGS films 315 and 325 are sequentially deposited on the i-ZnO films 313 and 323. Like the CIGS solar cell 200, a nanoparticle layer 330 is introduced between two cells.

The nanoparticle layer 330 of the CIGS solar cell 300 also increases the efficiency of the solar cell by facilitating the movement of electrons and holes in the same principle as the nanoparticle layer 330 of the CIGS solar cell 200. That is, both the lower cell and the upper cell of the CIGS solar cell 300 form an np junction, and as a result, a high energy barrier is formed by the pn junction at the interface, which may inhibit the movement of electrons and holes. The 330 lowers the energy barrier by minimizing the generation and diffusion of the depletion layer, thereby facilitating tunneling of electrons and holes, thereby increasing the efficiency of the solar cell.

4 is a process diagram illustrating a manufacturing process of the CIGS solar cell 200 of FIG. 2. Hereinafter, a manufacturing process of the substrate type tandem structure CIGS solar cell 200 of FIG. 2 will be described with reference to FIG. 4.

First, a molybdenum (Mo) film 212 is deposited on the substrate 211 as shown in FIG. 4A. The substrate 211 may be a transparent substrate such as a glass substrate or a plastic substrate, and the molybdenum film 212 may be deposited using a known deposition method such as sputtering or mechanical / chemical deposition.

Thereafter, as shown in FIG. 4B, a CIGS film 213 is deposited. The CIGS film 213 may be deposited using a co-evaporation method using four metal elements as a starting element, or may be deposited by screen printing using nanoparticles. The deposition thickness of the CIGS film 213 is about 1 to 3 m. In forming the CIGS film 213, CuInSe ₂ has an energy band gap of about 1.04 eV, high short-circuit current but low open-circuit voltage, and low efficiency, so that the amount of Ga is appropriately adjusted to adjust the energy band gap. Find the conditions that make the efficiency of

Next, as shown in Figs. 4C and 4D, the CdS film 214, the i-ZnO film 215, and the ZnO: Al film 216 are sequentially deposited as buffer layers. Since the energy band gap between the CIGS film 213 and the i-ZnO film 215 is large and the lattice constant difference is large, the CdS film 214 is used as the buffer layer. The CdS film 214 helps increase the efficiency of the solar cell by mitigating the energy band gap between the CIGS film 213 and the i-ZnO film 215 and reducing the lattice constant difference. The CdS film 214 is preferably deposited at about 50 nm, and may be replaced with another buffer material such as a zinc sulfide (ZnS) film or an indium oxide (In ₂ O ₃ ) film instead of the CdS film 214 as a buffer layer.

On the other hand, the i-ZnO film 215 may be deposited using a known deposition method such as sputtering, and the deposition thickness is suitably set to several tens of nanometers. The ZnO: Al film 216 is preferably deposited to a thickness of several hundred nanometers.

Next, as shown in FIG. 4E, a nanoparticle layer 230, which is a characteristic constitution of the present invention, is formed on the ZnO: Al film 216. The nanoparticle layer 230 may be formed by applying a colloidal solution containing metal nanoparticles, or may be formed by heat treatment after depositing a thin metal film of about 2 nm. As the metal nanoparticles included in the nanoparticle layer 230, gold (Au), silver (Ag), nickel (Ni), or the like may be used as described above. In addition, the density of the nanoparticle layer 230 may be appropriately selected within a range that does not prevent the passage of sunlight from the upper cell 220 to the lower cell 210 while minimizing depletion layer generation. Meanwhile, since metal particles included in the nanoparticle layer 230 may diffuse into the CIGS layer 223 at a temperature used in a subsequent process, the film quality thereof may be degraded, the conditions of the subsequent process and the types of the nanoparticles may be appropriately considered. You can choose.

After the nanoparticle layer 230 is formed, the upper cell 220 is formed thereon. First, as shown in FIG. 4F, a CIGS film 223 is deposited. As described above, in the substrate type tandem structure CIGS solar cell 200, the movement of electrons may be inhibited by a high energy barrier generated at the interface between the lower cell 210 and the upper cell 220. ), A high p-type copper (Cu) layer is first thinly deposited to a thickness of several tens of nanometers or less, thereby forming a depletion layer that may occur at the interface between the lower cell 210 and the upper cell 220. The diffusion into the CIGS film 223 can be prevented as much as possible. As a result, the tunneling movement of electrons and holes at the interface may be as free as possible, and the efficiency of the solar cell may be maximized with the introduction of the nanoparticle layer 230.

On the other hand, the band gap energy value of the CIGS film 223 is slightly higher than that of the lower layer so that light of a longer wavelength band can be transmitted through the lower layer, thereby further increasing the efficiency of the solar cell. As an example, the band gap energy value of the CIGS film 223 may be 1.6 eV, and the band gap energy value of the CIGS film 213 may be 1.2 eV.

Next, as shown in Fig. 4G, a CdS film 224, an i-ZnO film 225, and a ZnO: Al film 226 as a buffer layer are sequentially deposited. Since the deposition method of the films is the same as the deposition of the CdS film 214, the i-ZnO film 215, and the ZnO: Al film 216 of the lower cell 210, a description thereof will be omitted.

Thereafter, as shown in FIG. 4H, the production of the substrate type tandem structure CIGS solar cell 200 is formed by forming an antireflection film 227 and a grid electrode 240 on the ZnO: Al film 216. Is completed.

Magnesium fluoride (MgF ₂ ) may be used as the anti-reflection film 227, and an electron beam evaporation method may be used as the deposition method, and the deposition thickness is preferably about 100 nm. On the other hand, the grid electrode 240 may be formed using aluminum (Al) or nickel aluminum alloy (Ni / Al), and the like, in the case of aluminum, the thickness is about 1㎛ or more, in the case of nickel It is desirable that the thickness be several tens of nanometers.

In the manufacturing of the CIGS solar cell 200 described with reference to FIG. 4, if the process temperature is too high when the upper cell 220 is formed after the lower cell 210 is formed, the characteristics of the lower cell may be deteriorated. It is desirable to adjust the process temperature in consideration.

The fabrication of the super-straight type tandem structured CIGS solar cell 300 of FIG. 3 includes ZnO: Al films 312 and 322 and i-ZnO films 313 and 323 in both the lower cell 310 and the upper cell 320. Only the order of depositing the CdS films 314 and 324, and the CIGS films 315 and 325 are different, and the nanoparticle layer 330 is formed and deposited on the bottom cell 310, which is a feature of the present invention. Since the configuration of forming the upper cell 320 is the same, a description of the manufacturing process thereof will be omitted.

5 is a diagram illustrating an energy band of a CIGS solar cell. First, FIG. 5A is an energy band diagram of a single cell structure CIGS solar cell, FIG. 5B is an energy band diagram of a conventional tandem structure CIGS solar cell, and FIG. 5C is an energy band diagram of a tandem structure CIGS solar cell according to the present invention. .

As described above, in the CIGS solar cell, as a buffer layer between the CIGS film and the ZnO film in order to alleviate the large energy band gap difference and the large lattice constant between the CIGS film and the ZnO film to increase the efficiency of the solar cell. A CdS film is formed. As shown in FIG. 5A, the CdS film serves as a buffer layer, thereby lowering an energy barrier between the i-ZnO film and the CIGS film, thereby freeing tunneling movement of electrons and holes. The efficiency of can be increased.

Meanwhile, referring to FIG. 5, since the substrate-type tandem structure CIGS solar cell is stacked in the pn direction in both the lower layer cell and the upper layer cell, np junction is performed at the interface between the lower cell and the upper cell, as illustrated in FIG. 5. High energy barriers such as As a result, the tunneling movement of electrons and holes forming a p + -n + junction at a high concentration at the interface between the lower cell and the upper cell may be inhibited, thereby lowering the efficiency of the solar cell.

5C shows the result of lowering the energy barrier between the lower and upper cells of the tandem structured CIGS solar cell due to the introduction of the nanoparticle layer. As described above, the energy barrier is lowered by minimizing the depletion layer formation and diffusion by the nanoparticle layer composed of nano-sized metal particles. As a result, the tunneling movement of electrons and holes is facilitated, and thus the solar cell The efficiency of the becomes high.

The present invention has been described above in connection with specific embodiments of the present invention, but this is only an example and the present invention is not limited thereto. Those skilled in the art can change or modify the described embodiments without departing from the scope of the present invention, and such changes or modifications are within the scope of the present invention. In addition, each component described herein may be easily selected and replaced by various components known to those skilled in the art. Those skilled in the art can also omit some of the components described herein without adding performance degradation or add components to improve performance. Therefore, the scope of the present invention should be determined not by the embodiments described, but by the claims and their equivalents.

1 is a cross-sectional view showing the structure of a conventional single cell CIGS solar cell.

2 is a cross-sectional view showing the configuration of a CIGS solar cell according to an embodiment of the present invention.

3 is a cross-sectional view showing the configuration of a CIGS solar cell according to another embodiment of the present invention.

4 is a process chart showing a manufacturing process of the CIGS solar cell of FIG.

5A is an energy band diagram of a CIGS solar cell with a single cell structure.

5B is an energy band diagram of a conventional tandem structure CIGS solar cell.

5c is an energy band diagram of a tandem structured CIGS solar cell according to the present invention.

<Description of the symbols for the main parts of the drawings>

210, 310: lower solar cell

220, 320: upper solar cell

211, 311: substrate

213, 223, 315, 325: CIGS membrane

214, 224, 314, 324: CdS membrane

215, 225, 313, 323: i-ZnO membrane

216, 226, 312, 322: ZnO: Al film

230, 330: nanoparticle layer

Claims (14)

In a tandem structure CIGS solar cell formed by stacking a lower CIGS solar cell and an upper CIGS solar cell sequentially, Tandem structure CIGS solar cell comprising a nanoparticle layer consisting of metal nanoparticles at the interface between the lower CIGS solar cell and the upper CIGS solar cell. The method of claim 1, Tandem structure CIGS solar cell, characterized in that the material of the metal nanoparticles included in the nanoparticle layer is at least one of gold (Au), silver (Ag), nickel (Ni). The method of claim 1, The CIGS solar cell of the tandem structure CIGS solar cell, characterized in that it comprises a CIGS film, a buffer layer, and a zinc oxide (ZnO) film is laminated in sequence. The method of claim 3, Tandem structure CIGS solar cell, characterized in that the CIGS film included in the upper CIGS solar cell has a larger energy band gap than the CIGS film included in the lower CIGS solar cell. The method of claim 1, The CIGS solar cell of the tandem structure CIGS solar cell, characterized in that it comprises a zinc oxide (ZnO) film, a buffer layer, and a zinc oxide (ZnO) film each stacked in turn. The method of claim 5, Tandem structure CIGS solar cell, characterized in that the CIGS film contained in the lower CIGS solar cell has a larger energy band gap than the CIGS film included in the upper CIGS solar cell. The method according to claim 3 or 5, The buffer layer is a tandem structure CIGS solar cell, characterized in that one of the cadmium sulfide (CdS) film, zinc sulfide (ZnS) film, indium oxide (In ₂ O ₃ ) film. In the manufacturing method of the tandem structure CIGS solar cell formed by stacking the lower CIGS solar cell and the upper CIGS solar cell in order, Stacking the lower CIGS solar cell; Forming a nanoparticle layer composed of metal nanoparticles on the lower CIGS solar cell; And And depositing the upper CIGS solar cell on the nanoparticle layer. The method of claim 8, The material of the metal nanoparticles included in the nanoparticle layer is at least one or more of gold (Au), silver (Ag), nickel (Ni) manufacturing method of a tandem structure CIGS solar cell. The method of claim 8, Forming the nanoparticle layer, tandem structure CIGS solar cell manufacturing method comprising the step of applying a colloidal solution containing the metal nanoparticles. The method of claim 8, Forming the nanoparticle layer, Depositing a metal thin film; And And heat treating the metal thin film to form the metal nanoparticles. The method of claim 8, Stacking the bottom CIGS solar cell and stacking the top CIGS solar cell, tandem structure CIGS solar, comprising the step of laminating a CIGS film, a buffer layer, and a zinc oxide (ZnO) film in sequence Method for producing a battery. The method of claim 8, Stacking the bottom CIGS solar cell and stacking the top CIGS solar cell, tandem structure CIGS solar, comprising the step of sequentially stacking a zinc oxide (ZnO) film, a buffer layer, and a CIGS film Method for producing a battery. The method according to claim 12 or 13, The buffer layer is a cadmium sulfide (CdS) film, zinc sulfide (ZnS) film, indium oxide (In ₂ O ₃ ) film manufacturing method of a tandem structure CIGS solar cell, characterized in that.

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