KR101412150B1 - Tandem structure cigs solar cell and method for manufacturing the same - Google Patents

Abstract

A tandem-structured CIGS solar cell and its manufacturing method are disclosed. In the tandem-structured CIGS solar cell of the present invention, a metal nanoparticle layer is formed between two cells, thereby enhancing the mobility of energy electrons and holes at the cell boundary surface, thereby maximizing the efficiency.

The tandem-structured CIGS solar cell of the present invention comprises a lower CIGS solar cell and an upper CIGS solar cell stacked in that order, and the lower CIGS solar cell and the upper CIGS solar cell are composed of metal nanoparticles And a nanoparticle layer.

CIGS solar cell, tandem structure, nanoparticle, energy band, energy barrier

Description

TECHNICAL FIELD [0001] The present invention relates to a tandem structure CIGS solar cell and a manufacturing method thereof,

The present invention relates to a tandem-structured CIGS solar cell and a manufacturing method thereof. More specifically, by forming a metal nanoparticle layer between two CIGS solar cells included in a tandem-structured CIGS solar cell, the energy barrier of the cell interface is lowered to allow tunneling movement of electrons and holes, To a tandem-structured CIGS solar cell and a manufacturing method thereof.

In recent years, interest in new and renewable energy has been rising due to rising oil prices, global environmental problems, depletion of fossil energy, waste treatment of nuclear power generation, and location of new power plants. Research and development of batteries is actively under way.

A solar cell is a device that converts light energy into electrical energy by using photovoltaic effect. The solar cell is divided 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 independently used as main power sources for electronic clocks, radios, unmanned lighthouses, satellites, rockets, etc., and are also used as auxiliary power sources in connection with commercial AC power systems. Recently, The interest in solar cells is increasing.

In such a solar cell, it is very important to increase the conversion efficiency that is related to the ratio of converting incident solar light into electrical energy. Various studies have been made to increase the conversion efficiency. Techniques for improving the conversion efficiency by actively incorporating a thin film having a high light absorption coefficient into a solar cell have been actively developed.

CIGS (Copper Indium Galium Selenide) has been introduced as a material having a high light absorption coefficient, and it has been found that high conversion efficiency can be obtained by using such CIGS in the manufacture of a thin film solar cell. As a result, film-type CIGS solar cells are emerging as an alternative energy source with high efficiency.

FIG. 1 shows the structure of a conventional single cell CIGS solar cell. 1, a 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, i (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. At this time, the energy bandgap difference between the CIGS film 130 and the i-ZnO film 150 is relatively large and the efficiency of the solar cell may be lowered. To prevent this, a cadmium sulfide (CdS) film 140 are introduced between the CIGS film 130 and the i-ZnO film 150. The cadmium sulfide (CdS) film 140 improves the efficiency of the solar cell by alleviating the difference in the energy band gap and the lattice constant between the CIGS film 130 and the i-ZnO film 150.

In order to further increase the efficiency of CIGS solar cells, two single-cell CIGS solar cells were stacked. The structure of the CIGS solar cell formed by laminating the two cells is called a tandem structure.

However, such a tandem-structured CIGS solar cell has an n-p junction or a p-n junction at its interface since both the lower cell and the upper cell have a p-n structure or an n-p structure. As a result, the energy barrier at the interface between the two cells is formed to be very high, which hinders the movement of electrons and holes. Accordingly, there has been a problem in that the efficiency of the solar cell can not be maximized even with the tandem structure.

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

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a tandem-structured CIGS solar cell in which the energy barrier at the interface between two cells in a tandem-structured CIGS solar cell is enhanced to improve the mobility of electrons and holes, And the like.

Another object of the present invention is to provide a tandem structure capable of maximizing the efficiency by facilitating tunneling movement of electrons and holes by lowering the energy barrier by introducing metal nanoparticles at the interface between two cells of a tandem structure CIGS solar cell And to provide a method of manufacturing a CIGS solar cell.

According to an aspect of the present invention, there is provided a tandem-structured CIGS solar cell including a lower CIGS solar cell and an upper CIGS solar cell stacked in that order, And a nanoparticle layer composed of metal nanoparticles on the interface between the upper CIGS solar cell and the upper CIGS solar cell.

The tandem solar cell of the present invention is not necessarily limited to the structure described above, and may include a plurality of double solar cells, in which a lower CIGS solar cell and an upper CIGS solar cell are sequentially stacked, .

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 cell may include a CIGS film, a buffer layer, and a zinc oxide (ZnO) film stacked in order, wherein the CIGS film included in the upper CIGS solar cell is larger than the CIGS film included in the lower CIGS solar cell It can have an energy bandgap.

The CIGS solar cell may include a zinc oxide (ZnO) layer, a buffer layer, and a zinc oxide (ZnO) layer stacked in that order, and the CIGS layer included in the lower CIGS solar cell may be included in the upper CIGS solar cell It is possible to have a larger energy bandgap 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 aspect of the present invention, there is provided a method of manufacturing a tandem-structured CIGS solar cell in which a lower CIGS solar cell and an upper CIGS solar cell are sequentially stacked, Forming a nanoparticle layer of metal nanoparticles on the lower CIGS solar cell, and laminating the upper CIGS solar cell on the nanoparticle layer, Wherein the CIGS solar cell is 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).

The forming of the nanoparticle layer may include applying a colloid solution containing the metal nanoparticles.

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

The step of laminating the lower CIGS solar cell and the step of laminating the upper CIGS solar cell may include a step of sequentially laminating a CIGS film, a buffer layer, and a zinc oxide (ZnO) film.

The step of laminating the lower CIGS solar cell and the step of laminating the upper CIGS solar cell may include a step of laminating a zinc oxide (ZnO) film, a buffer layer, and a CIGS film in order.

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, by introducing metal nanoparticles at the interface between two cells in a tandem-structured CIGS solar cell, the energy barrier at the interface can be lowered to freely tunnel electrons and holes, A maximized tandem structure CIGS solar cell can be obtained.

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

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

2, the CIGS solar cell 200 of the present invention includes a nanoparticle layer 230 introduced between two cells of a substrate tandem-structured CIGS solar cell .

In order to increase the efficiency of the CIGS solar cell, a tandem CIGS solar cell in which two cells are stacked mechanically or integrally is widely used, and a tandem CIGS solar cell is again divided into a substrate type and a superstrate type .

The substrate tandem structure refers to a stack of a CIGS film as a buffer layer and a single cell CIGS solar cell formed by depositing a ZnO film as a window layer for absorbing solar light in this order on a CIGS film. The superstrate type tandem structure is a substrate type Cell CIGS solar cell is formed by sequentially depositing a ZnO film as a window layer and depositing a CdS film and a CIGS film as a buffer layer thereon.

2 is a substrate type tandem-structured CIGS solar cell among the tandem structures, and a CdS film (214, 224) film and an i-ZnO film (CIGS film) 215, and 225 are deposited in this order on the substrate 210. The nanoparticle layer 230 is introduced between the two cells.

In a typical tandem solar cell, two cells, that is, a lower cell and an upper cell, have different directions through the interface. 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 due to the energy barrier at this time can not be avoided. As a result, even if a CIGS solar cell is manufactured in a tandem structure, sufficient efficiency can not be obtained.

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

More 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, + ≫ + doped at a high concentration on the interface between the upper cell 220 and the upper cell 220, and the movement of electrons and holes may be hindered by a high energy barrier due to the above-mentioned reasons. The nanoparticle layer 230 composed of the metal particles of the nanoparticles minimizes the generation of the depletion layer in bonding with the semiconductor. As a result, the thickness of the energy barrier becomes thin, so that the tunneling movement of electrons and holes having a high concentration of p + -n + junction can easily occur.

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

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

The CIGS solar cell 300 shown in FIG. 3 is a super straight tandem structure CIGS solar cell. Like the CIGS solar cell 200 shown in FIG. 2, the nanoparticle layer 330 is introduced between two cells .

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, A nanoparticle layer 330 is introduced between two cells, such as a CIGS solar cell 200.

The nanoparticle layer 330 of the CIGS solar cell 300 also facilitates the movement of electrons and holes on the same principle as the nanoparticle layer 330 of the CIGS solar cell 200, thereby enhancing the efficiency of the solar cell. That is, both the lower cell and the upper cell of the CIGS solar cell 300 have an np junction, and due to the pn junction at the interface, a high energy barrier may be formed to inhibit the movement of electrons and holes. (330) minimizes the generation and diffusion of a depletion layer to lower the energy barrier, thereby facilitating tunneling of electrons and holes, thereby increasing the efficiency of the solar cell.

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

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

Thereafter, as shown in FIG. 4B, a CIGS film 213 is deposited. The CIGS film 213 may be deposited using a simultaneous evaporation method using four metal elements as a starting element, or may be deposited by a screen printing method using nanoparticles. The deposition thickness of the CIGS film 213 is about 1 to 3 mu m. Method for forming a CIGS film (213), CuInSe ₂ is about 1.04eV energy band gap, by the optimum short-circuit current is low, since setting the amount of addition of Ga is high, but the lower the efficiency of the open-circuit voltage by appropriately adjusting the energy bandgap Can be found.

Next, as shown in Figs. 4C and 4D, a CdS film 214, an i-ZnO film 215, and a ZnO: Al film 216 are sequentially deposited as a buffer layer. 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 a buffer layer. The CdS film 214 helps increase the efficiency of the solar cell by reducing the energy bandgap between the CIGS film 213 and the i-ZnO film 215 and reducing the lattice constant difference. The CdS film 214 is preferably deposited to a thickness of 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 can be deposited using a known deposition method such as a sputtering method, 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 feature of the present invention, is formed on the ZnO: Al film 216. The nanoparticle layer 230 may be formed by applying a colloid solution containing metal nanoparticles, or may be formed by depositing a thin metal film of about 2 nm and then heat-treating the thin metal film. 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 can be appropriately selected within a range that does not hinder the passage of sunlight from the upper cell 220 to the lower-layer cell 210 while minimizing the generation of depletion layers. On the other hand, since the metal particles included in the nanoparticle layer 230 are diffused into the CIGS layer 223 at a temperature used in a subsequent process, the quality of the metal particles may be lowered. Therefore, conditions of the subsequent process and kinds of nanoparticles You can choose.

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

On the other hand, by making the band gap energy value of the CIGS film 223 slightly higher than that of the lower layer, light of a long wavelength band can be transmitted to the lower layer well, 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 CdS film 214, the i-ZnO film 215, and the ZnO: Al film 216 of the lower cell 210 are deposited, the description thereof will be omitted.

4H, an antireflection film 227 and a grid electrode 240 are formed on the ZnO: Al film 216, thereby forming the substrate tandem structure CIGS solar cell 200 Is completed.

As the antireflection film 227, magnesium fluoride (MgF ₂ ) can be used. As the deposition method, an electron beam evaporation method or the like can be used, and the deposition thickness is preferably about 100 nm. On the other hand, the grid electrode 240 may be formed using aluminum (Al) or a nickel aluminum alloy (Ni / Al). In case of aluminum, the thickness of the grid electrode 240 is about 1 μm or more, It is preferable to set the thickness to several tens of nanometers.

In the fabrication of the CIGS solar cell 200 described with reference to FIG. 4, if the process temperature is excessively increased 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 preferable to adjust the process temperature.

The fabrication of the superstrate type tandem structure CIGS solar cell 300 of FIG. 3 is performed by using ZnO: Al films 312 and 322, i-ZnO films 313 and 323 in both the lower cell 310 and the upper cell 320, The CdS films 314 and 324 and the CIGS films 315 and 325 are different from each other in order to form the nanoparticle layer 330 after deposition of the lower cell 310, The upper layer cell 320 is formed in the same manner as the upper layer cell 320. Therefore, a description of its manufacturing process will be omitted.

5 is a diagram showing the energy band of a CIGS solar cell. 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, in order to increase the efficiency of the solar cell by alleviating the difference in the large energy bandgap difference and the large lattice constant between the CIGS film and the ZnO film, Thereby forming a CdS film. As shown in FIG. 5A, since the CdS film serves as a buffer layer, the energy barrier between the i-ZnO film and the CIGS film is lowered, so that the tunneling movement of electrons and holes can be freely performed, Can be increased.

Referring to FIG. 5, since the conventional substrate-type tandem-structured CIGS solar cell is stacked in the pn direction in both the lower-layer cell and the upper-layer cell, the np junction is formed at the interface between the lower cell and the upper cell, Lt; / RTI > is formed. As a result, the tunneling movement of electrons and holes forming a p + -n + junction at a high concentration on the interface between the lower cell and the upper cell is inhibited, and the efficiency of the solar cell can be lowered.

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

Although the present invention has been described in connection with the specific embodiments of the present invention, it is to be understood that the present invention is not limited thereto. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. In addition, each of the elements described herein can be readily selected and substituted for various components known to those skilled in the art. Those skilled in the art will also appreciate that some of the components described herein can be omitted without degrading performance or adding components to improve performance. Therefore, the scope of the present invention should be determined by the appended claims and equivalents thereof, not by the embodiments described.

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

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

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

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

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

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 Related Art

210, and 310: a lower solar cell

220, 320: upper solar cell

211, 311: substrate

213, 223, 315, 325: CIGS film

214, 224, 314, 324: CdS film

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

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

230, 330: nanoparticle layer

Claims (14)

1. A tandem-structured CIGS solar cell comprising a lower CIGS solar cell and an upper CIGS solar cell stacked in that order, And a nanoparticle layer composed of metal nanoparticles on the interface between the lower CIGS solar cell and the upper CIGS solar cell, The upper and lower CIGS solar cells each include a CISG layer, a buffer layer, and a zinc oxide (ZnO) layer, The CIGS film of one of the upper and lower CIGS solar cell cells and the other zinc oxide film are located close to each other, The nanoparticle layer between the CIGS film of one of the upper and lower CIGS solar cells and the other zinc oxide film is formed, Wherein the CIGS film of one of the upper and lower CIGS solar cells has a p-type copper layer adjacent to the nanoparticles. The method according to claim 1, Wherein the material of the metal nanoparticles included in the nanoparticle layer is at least one of gold (Au), silver (Ag), and nickel (Ni). The method according to claim 1, Wherein the upper and lower CIGS solar cells each have a CIGS layer, a buffer layer, and a zinc oxide (ZnO) layer stacked in that order. The method of claim 3, Wherein the CIGS film included in the upper CIGS solar cell has a larger energy bandgap than the CIGS film included in the lower CIGS solar cell. The method according to claim 1, Wherein the upper and lower CIGS solar cells each have a zinc oxide (ZnO) layer, a buffer layer, and a CIGS layer stacked in that order. 6. The method of claim 5, Wherein the CIGS film included in the lower CIGS solar cell has a larger energy bandgap than the CIGS film included in the upper CIGS solar cell. The method according to claim 3 or 5, Wherein the buffer layer is one of a cadmium sulfide (CdS) film, a zinc sulfide (ZnS) film, and an indium oxide (In ₂ O ₃ ) film. A method of manufacturing a tandem-structured CIGS solar cell in which a lower CIGS solar cell and an upper CIGS solar cell are sequentially stacked, Stacking the lower CIGS solar cell; Forming a nanoparticle layer composed of metal nanoparticles on the lower CIGS solar cell; And And laminating the upper CIGS solar cell on the nanoparticle layer, The upper and lower CIGS solar cells each include a CISG layer, a buffer layer, and a zinc oxide (ZnO) layer, The CIGS film of one of the upper and lower CIGS solar cell cells and the other zinc oxide film are located close to each other, The nanoparticle layer between the CIGS film of one of the upper and lower CIGS solar cells and the other zinc oxide film is formed, Wherein the CIGS film of one of the upper and lower CIGS solar cells has a p-type copper layer adjacent to the nanoparticles. 9. The method of claim 8, Wherein the material of the metal nanoparticles included in the nanoparticle layer is at least one of gold (Au), silver (Ag), and nickel (Ni). 9. The method of claim 8, Wherein the step of forming the nanoparticle layer comprises the step of applying a colloid solution containing the metal nanoparticles. 9. The method of claim 8, Wherein forming the nanoparticle layer comprises: Depositing a metal thin film; And And forming the metal nanoparticles by heat-treating the metal thin film. 9. The method of claim 8, The step of laminating the lower CIGS solar cell and the step of laminating the upper CIGS solar cell each include the step of sequentially laminating the CIGS film, the buffer layer, and the zinc oxide (ZnO) film Method of manufacturing tandem structure CIGS solar cell. 9. The method of claim 8, The step of laminating the lower CIGS solar cell and the step of laminating the upper CIGS solar cell each include the step of sequentially laminating the zinc oxide (ZnO) film, the buffer layer, and the CIGS film Method of manufacturing tandem structure CIGS solar cell. The method according to claim 12 or 13, Wherein the buffer layer is one of a cadmium sulfide (CdS) film, a zinc sulfide (ZnS) film, and an indium oxide (In ₂ O ₃ ) film.

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