KR101300642B1 - Solar cell - Google Patents

Abstract

The present invention relates to a superstrate type CIGS thin film solar cell, comprising: a substrate; A window layer provided on the substrate; A protective layer provided on the window layer; A buffer layer provided on the protective layer; A light absorption layer provided on the buffer layer; And a back electrode provided on the light absorbing layer, wherein the window layer is prevented from being deteriorated at a high temperature in the process of forming the light absorbing layer, thereby preventing a decrease in efficiency and lifespan of the solar cell.

Description

Solar cell {Solar cell}

The present invention relates to a solar cell, and more particularly, to a superstrate type CIGS thin film solar cell capable of suppressing deterioration of characteristics of a window layer.

In general, ternary thin films of I-III-VI ₂ compounds such as CuInSe ₂ (hereinafter referred to as "CIS") or CuIn _{1 - x} Ga _x Se ₂ (hereinafter referred to as "CIGS") are actively used as absorbing layers for solar cells. It is one of the compound semiconductors under study. The CIS or CIGS compound semiconductors used in solar cells have an energy bandgap of 1 to 1.4 eV at room temperature and a linear light absorption coefficient of 1 × 10 ^-5 cm ^{-1, which} is about 10 to 100 times larger than other semiconductors. It is attracting attention as an absorber of solar cells.

In particular, these CIS or CIGS-based thin-film solar cells, unlike conventional solar cells using silicon crystals can be manufactured to a thickness of less than 10 microns and has a stable characteristic even when used for a long time. In addition, experimentally the highest energy conversion efficiency is 20.3%, the energy conversion efficiency is superior to other thin-film solar cells, it is highly commercialized as a low-cost high-efficiency solar cell that can replace silicon crystalline solar cells.

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

Referring to FIG. 1, in the CIGS thin film solar cell, the back electrode 110, the light absorption layer 120, the buffer layer 130, and the window layer 140 are sequentially stacked on the substrate 100, and the window layer 140 is formed. It consists of a structure which injects sunlight through the direction in which it is formed. Accordingly, in order to protect the window layer 140 from foreign substances or moisture in the air, an additional protective layer 150 is formed on the window layer 140 or encapsulation using glass and an adhesive layer. , 160).

However, if the additional process is performed as described above, there is a problem in that the overall configuration of the solar cell becomes complicated and the manufacturing process becomes complicated. In addition, the encapsulation using glass increases the overall weight of the solar cell and increases the rigidity of the solar cell, thereby limiting its use as a flexible solar cell having flexibility. This will occur.

In order to solve this problem, in forming a solar cell, a superstrate-type solar cell may be manufactured in which a window layer is first formed on the substrate and then a light absorption layer is formed thereafter. The solar cell of such a structure has an advantage of simplifying the structure because it is not necessary to further form a protective layer or encapsulation on the window layer in order to protect against foreign matters or moisture in the air. In addition, the superstrate-type solar cell has an advantage that it can have a light weight (flexibility) and flexibility compared to the substrate type solar cell.

However, the solar cell of such a structure is commonly applied to silicon thin film solar cells. When applied to CIGS thin film solar cells, in the process of forming the light absorbing layer at a high temperature of 500 ° C. or higher, the window layer already formed under the light absorbing layer is degraded by the high temperature, thereby reducing the transmittance and conductivity, which are required characteristics of the window layer. Because it becomes. That is, the window layer is usually formed of a transparent conductive oxide (TCO), and the TCO has a high conductivity due to the oxygen vacancies formed therein. However, in the process of forming the light absorbing layer at a high temperature, impurities such as copper, indium, gallium, and selenium penetrate into the pores, resulting in a decrease in conductivity, resulting in a problem of deterioration in efficiency and lifespan of the solar cell.

KR 0642196 B1 KR 2011-0039777 A

The present invention provides a super-straight type CIGS thin film solar cell capable of a high temperature process without deteriorating the window layer.

In addition, the present invention eliminates encapsulation for protecting the window layer, thereby providing a flexible solar cell having a light weight and flexibility.

A solar cell according to the present invention includes a substrate; A window layer provided on the substrate; A protective layer provided on the window layer; A buffer layer provided on the protective layer; A light absorption layer provided on the buffer layer; And a rear electrode provided above the light absorption layer.
In addition, the solar cell according to the present invention, the substrate; A window layer provided on the substrate; A buffer layer provided on the window layer; A light absorption layer provided on the buffer layer; And a rear electrode provided on the light absorbing layer, and protective layers may be provided on the upper and lower portions of the window layer, respectively.

Here, a protective layer may be further provided between the substrate and the window layer, and the protective layer may be formed of one or more materials selected from the group consisting of TiO, TaO, TiN, and TaN.

In addition, the substrate may be formed of a light transmissive material.

The window layer may be formed of zinc oxide (ZnO), gallium oxide (GaO), indium oxide (InO), tin oxide (SnO), or a combination thereof, and the buffer layer may include CdS, ZnS, In (O, S). ) Or Zn (O, S).

In addition, the light absorption layer is CuInS ₂ (CIS), CuGaS ₂ (CGS), CuInSe ₂ (CISe), CuGaSe ₂ (CGSe), CuAlSe ₂ (CASe), CuInTe ₂ (CITe), CuGaTe ₂ (CGTe), Cu ( In, Ga) S ₂ (CIGS), Cu (In, Ga) Se ₂ (CIGSe), Cu ₂ ZnSnS ₄ (CZTS) and may be formed of one or more selected from the group consisting of CdTe, the back electrode May be formed of molybdenum (Mo).

In the solar cell according to the embodiment of the present invention, a protective film is formed on the window layer in the superstrate structure to prevent impurities from penetrating into the window layer in a high temperature process. Through this, it is possible to prevent the window layer from deteriorating even at a high temperature of 500 ° C. or more at which the light absorbing layer is formed, thereby preventing the efficiency and life of the solar cell.

In addition, the solar cell according to an embodiment of the present invention, by forming a window layer on the substrate of the transparent material, and then to protect the window layer after the solar cell is formed by forming a light absorption layer and a back electrode for absorbing light Encapsulation can be eliminated, providing a lightweight and flexible solar cell.

1 is a cross-sectional view showing the structure of a solar cell according to the prior art.
2 is a cross-sectional view showing the structure of a solar cell according to an embodiment of the present invention.
3 is a cross-sectional view showing the structure of a solar cell according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments without departing from the gist of the present invention.

Thin-film solar cells are largely divided into a substrate type and a superstrate type. The substrate type solar cell has a structure in which a back electrode, a light absorption layer, a window layer, and the like are sequentially stacked on the substrate, and light is incident on the window layer. In contrast, the superstrate type solar cell is a structure in which a window layer, a light absorbing layer, a back electrode, and the like are sequentially stacked on the light transmitting substrate so that light enters the substrate side.

Embodiment of this invention demonstrated below corresponds to a super-straight type solar cell.

2 is a cross-sectional view showing the structure of a solar cell according to an embodiment of the present invention, Figure 3 is a cross-sectional view showing another modified example of FIG.

2, a solar cell according to an embodiment of the present invention includes a substrate 200, a window layer 210 provided on the substrate 200, and a protective layer provided on the window layer 210. And a buffer layer 230 provided on the passivation layer 220, a light absorbing layer 240 provided on the buffer layer 230, and a back electrode 250 provided on the light absorbing layer 240. It is configured by.

In a solar cell according to an embodiment of the present invention, unlike a substrate type solar cell in which a back electrode is first formed on a substrate, a window layer 210 is formed on the substrate 200, and a light absorption layer is formed on the solar cell. 240 and the back electrode 250 are formed. Through such a configuration, light is incident through the substrate 200 side.

Therefore, the substrate 200 is preferably formed of a light transmissive material that can transmit light, and such a material may be glass, a transparent polymer, or the like. In addition, since the substrate 200 is exposed to the external environment, the substrate 200 may be formed of a material having durability against an external environment such as a gaseous state or an air pollutant. In addition, when glass is used as the substrate 200, manufacturing cost can be reduced by using sodaime glass which is relatively inexpensive.

The window layer 210 is an n-type semiconductor and functions as a transparent electrode on the front of the solar cell. The window layer 210 has a high light transmittance and high electrical conductivity, zinc oxide (ZnO), gallium oxide (GaO), and indium oxide. (InO), tin oxide (SnO), or the like, or a composite thereof. More specifically, the window layer 210 may be formed by RF sputtering, DC sputtering, reactive sputtering using oxygen, chemical vapor deposition using metals, or the like using the above materials.

As such, when the window layer 210 is directly formed on the substrate 200, the substrate 200 serves to protect the window layer 210 from moisture or air pollutants. Through such a configuration, additional processes such as encapsulation after solar cell manufacturing may be excluded. Therefore, encapsulation may prevent the overall weight of the solar cell from increasing, and may implement a flexible solar cell having flexibility.

When the formation of the window layer 210 is completed, the protective layer 220 is formed on the window layer 210. The protective layer 220 suppresses deterioration of the window layer 210 due to high temperature when the light absorption layer 240 is formed. That is, the light absorption layer 240 is usually formed at a high temperature of 500 ° C. or higher, and the protective layer 220 is a window layer 210 in a high temperature process for forming the light absorption layer 240, such as copper, indium, gallium, selenium, and the like. Used as a barrier to prevent impurities from penetrating. As a result, a decrease in transmittance or conductivity of the window layer 210 may be suppressed to prevent a decrease in efficiency or a lifespan of the solar cell.

As the protective layer 220, a stable material having high light transmittance and electrical conductivity, being thermally stable and having little reactivity with selenium (Se) in CIGS may be used. As such a material, an oxide-based material such as TiO or TaO or a nitride-based material such as TiN or TaN may be used. When the material is used as the protective layer 220, the reflectance may be reduced due to the difference in refractive index between the substrate 200 or the window layer 210, thereby increasing the transmittance.

Meanwhile, as shown in FIG. 3, the protective layer 222 may be further formed on the substrate 200 before the window layer 210 is formed. As such, by forming the protective layers 220 and 222 on the upper and lower portions of the window layer 210, the transmittance or conductivity of the window layer 210 may be effectively prevented.

In the buffer layer 230, the window layer 210, which is an n-type semiconductor, and the light absorbing layer 240, which is a p-type semiconductor, form a pn junction. These two materials form a good junction because the difference in lattice constant and energy band gap is large. As the layer formed for the purpose, a material in which the band gap is located between the two materials can be used. In the exemplary embodiment of the present invention, CdS, ZnS, In (O, S), Zn (O, S), or the like is used as the buffer layer 230. In the case where the buffer layer 230 is used as CdS, CdS forms an appropriate amount of Cd ++ and S-- ions in the solution and adjusts the temperature of the solution so that the product of each ion concentration is larger than the solubility of the solution in the form of CdS. It may be formed through a chemical bath deposition (CBD) method using the property of precipitation.

The light absorption layer 240 absorbs sunlight incident from the substrate 200 side, and CuInS ₂ (CIS), CuGaS ₂ (CGS), CuInSe ₂ (CISe), CuGaSe ₂ (CGSe), and CuAlSe ₂ ( CASe), CuInTe ₂ (CITe), CuGaTe ₂ (CGTe), Cu (In, Ga) S ₂ (CIGS), Cu (In, Ga) Se ₂ (CIGSe), Cu ₂ ZnSnS ₄ (CZTS), CdTe, etc. Chalcogenide compounds are exemplified. In an embodiment of the present invention, CIGS was used as the light absorption layer 240. CIGS may be deposited using a co-evaporation method using four metal elements (Cu, In, Ga, Se) as starting elements, and sputtering and selenization of these metal elements or compounds to form a thin film. May be In addition, after the chalcogenide compound or precursor nanoparticles are prepared without using the vacuum equipment as described above, the thin film may be formed by a wet method such as a printing process.

Nickel (Ni) and copper (Cu) have been used as the back electrode 250, but molybdenum (Mo) is most widely used. This is because of high electrical conductivity of molybdenum (Mo), ohmic bonding with the light absorbing layer 240, and high temperature stability under a selenium (Se) atmosphere.

The back electrode 250 may be formed through various methods such as sputtering or evaporation. The thickness of the back electrode 250 may be several hundred nanometers or more.

In the solar cell according to the embodiment of the present invention configured as described above, the window layer through which light is incident is formed on the substrate, and thus the window layer may be prevented from being deteriorated or damaged by an external environment even without encapsulation. have. Through this, it is possible to suppress the increase in the weight of the solar cell and at the same time limit the use of the flexible solar cell.

In addition, by forming protective layers on the upper and lower portions of the window layer, it is possible to prevent impurities from penetrating into the window layer in the high temperature process of forming the light absorbing layer, thereby preventing the efficiency and life of the solar cell from being lowered.

Although the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. Therefore, the scope of the present invention should not be limited by the described embodiments, but should be defined by the appended claims and equivalents thereof.

100, 200: substrate 110, 250: back electrode
120, 240: light absorption layer 130, 230: buffer layer
140, 210: window layer 150, 220, 222: protective layer

Claims (8)

Claims [1]
A window layer provided on the substrate;
A protective layer provided on the window layer;
A buffer layer provided on the protective layer;
A light absorption layer provided on the buffer layer; And
A rear electrode provided above the light absorption layer;
≪ / RTI > Claims [1]
A window layer provided on the substrate;
A buffer layer provided on the window layer;
A light absorption layer provided on the buffer layer; And
A rear electrode provided above the light absorption layer;
/ RTI >
Solar cells provided with a protective layer on the upper and lower portions of the window layer, respectively. The method according to claim 1 or 2,
The substrate is a solar cell formed of a light transmissive material. The method according to claim 1 or 2,
The protective layer is a solar cell of at least one material selected from the group consisting of TiO, TaO, TiN and TaN. The method according to claim 1 or 2,
The window layer is zinc oxide (ZnO), gallium oxide (GaO), indium oxide (InO), tin oxide (SnO) or a composite thereof. The method according to claim 1 or 2,
The buffer layer is a CdS, ZnS, In (O, S) or Zn (O, S) solar cell. The method according to claim 1 or 2,
The light absorption layer is CuInS ₂ (CIS), CuGaS ₂ (CGS), CuInSe ₂ (CISe), CuGaSe ₂ (CGSe), CuAlSe ₂ (CASe), CuInTe ₂ (CITe), CuGaTe ₂ (CGTe), Cu (In, A solar cell formed of one or more selected from the group consisting of Ga) S ₂ (CIGS), Cu (In, Ga) Se ₂ (CIGSe), Cu ₂ ZnSnS ₄ (CZTS), and CdTe. The method according to claim 1 or 2,
The back electrode is a solar cell formed of molybdenum (Mo).

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