KR20130044850A - Solar cell and method of fabricating the same - Google Patents

Abstract

PURPOSE: A solar cell and a manufacturing method thereof are provided to improve photoelectric conversion efficiency by collecting electrons formed in a light absorbing layer through a front electrode layer including graphene. CONSTITUTION: A rear electrode layer(200) is arranged on a support substrate. A light absorbing layer(300) is arranged on the rear electrode layer. A front electrode layer(600) is arranged on the light absorbing layer and includes graphene. The front electrode layer includes a plurality of graphene layers and a plurality of metal oxide layers. The plurality of metal oxide layers and the plurality of graphene layers are alternatively deposited.

Description

SOLAR CELL AND METHOD OF FABRICATING THE SAME

An embodiment relates to a solar cell and a manufacturing method thereof.

A solar cell can be defined as a device that converts light energy into electric energy by using a photovoltaic effect that generates electrons when light is applied to a p-n junction diode. The solar cell can be classified into a silicon solar cell, a compound semiconductor solar cell represented by group I-III-VI or III-V, a dye-sensitized solar cell, and an organic solar cell, depending on materials used as a junction diode.

CIGS (CuInGaSe) solar cell, which is one of the I-III-VI family chalcopyrite compound semiconductors, has excellent light absorption, high photoelectric conversion efficiency even at a thin thickness, and excellent electro- It is emerging as an alternative solar cell.

CIGS solar cells must be resistant to moisture (H ₂ O) or oxygen (O ₂ ) from the outside, and solving these reliability problems is one of the important factors in CIGS solar cell performance. In general, CIGS solar cells penetrate moisture (H ₂ O) or oxygen (O ₂ ) into the solar cell through the interface of each layer, in particular, the interface between the front electrode layer and the adjacent layer. Meanwhile, the front electrode layer of the conventional CIGS solar cell uses zinc oxide (AZO) doped with aluminum, but AZO has advantages such as low resistance and high permeability, but penetration of moisture (H ₂ O) or oxygen (O ₂ ). There is a very weak disadvantage.

In addition, aluminum-doped zinc oxide (AZO) is deposited thick with a low power source in order to lower the resistance, which not only reduces the transmittance but also increases the process instability, material cost, and facility investment cost. In addition, as the width of the solar cell increases, the series resistance R _S of the front electrode layer increases, resulting in a decrease in electrical conductivity.

The embodiment is to provide a solar cell and a manufacturing method thereof having improved reliability and stability, and improved photoelectric conversion efficiency.

A solar cell according to an embodiment includes: a rear electrode layer disposed on a supporting substrate; A light absorbing layer disposed on the rear electrode layer; And a front electrode layer disposed on the light absorbing layer and including graphene.

A method of manufacturing a solar cell according to an embodiment includes forming a rear electrode layer on a supporting substrate; Forming a light absorbing layer on the back electrode layer; And forming a front electrode layer including graphene on the light absorbing layer.

The solar cell according to the embodiment provides a front electrode layer including graphene. The graphene not only has excellent mechanical strength, but also minimizes penetration of moisture (H ₂ O) or oxygen (O ₂ ) into the solar cell along the interface. That is, the solar cell according to the embodiment effectively contributes to securing the stability and reliability of the device by effectively protecting the solar cells from moisture and oxygen.

In addition, graphene is superior in electrical properties such as electrical conductivity and electron mobility than the conventional front electrode layer. Accordingly, the solar cell according to the embodiment may collect more electrons formed in the light absorbing layer as compared with the conventional front electrode layer, and the photoelectric conversion efficiency may be improved.

1 is a cross-sectional view showing a cross section of a solar cell according to the first embodiment.
2 is a cross-sectional view showing a cross section of the solar cell according to the second embodiment.
3 to 7 are cross-sectional views illustrating a method of manufacturing the solar cell according to the second embodiment.

In the description of the embodiments, where each substrate, layer, film, or electrode is described as being formed "on" or "under" of each substrate, layer, film, or electrode, etc. , “On” and “under” include both “directly” or “indirectly” other components. In addition, the upper or lower reference of each component is described with reference to the drawings. The size of each component in the drawings may be exaggerated for the sake of explanation and does not mean the size actually applied.

As used herein, the term "grapheme" refers to a graphene in which a plurality of carbon atoms are covalently linked to each other to form a polycyclic aromatic molecule, forming a layer or sheet form. The carbon atoms form a 6-membered ring as the basic repeating unit, but may further include a 5-membered ring and / or a 7-membered ring. Thus, the graphene appears as a single layer of covalently bonded carbon atoms (usually sp ² bonds). The graphene may have a variety of structures, such a structure may vary depending on the content of 5-membered and / or 7-membered rings that may be included in the graphene. The graphene may be formed of a single layer of graphene as described above, but they may be stacked with each other to form a plurality of layers. In general, the side ends of the graphene may be saturated with hydrogen atoms.

1 is a cross-sectional view showing a cross section of a solar cell according to the first embodiment. Referring to FIG. 1, the solar cell according to the embodiment includes a support substrate 100, a rear electrode layer 200, a light absorbing layer 300, a buffer layer 400, a high resistance buffer layer 500, and graphene. It includes a front electrode layer 600 including.

The support substrate 100 has a plate shape, and the back electrode layer 200, the light absorbing layer 300, the buffer layer 400, the high resistance buffer layer 500, the front electrode layer 600, and the graphene. The front electrode layer 600 including the graphene is supported.

The support substrate 100 may be an insulator. The support substrate 100 may be a glass substrate, a plastic substrate, or a metal substrate. In more detail, the support substrate 100 may be a soda lime glass substrate.

The support substrate 100 may be rigid or flexible. In more detail, the support substrate 100 may be a flexible substrate. For example, a flexible polymer or the like may be used as a material of the support substrate 100. The front electrode layer 600 of the solar cell according to the embodiment not only has excellent mechanical properties but also excellent flexibility, and when the support substrate 100 is a flexible material, the solar cell according to the embodiment has flexible characteristics. It can be used easily in the required area.

The back electrode layer 200 is disposed on the support substrate 100. The back electrode layer 200 is a conductive layer. The rear electrode layer 200 may be formed of any one of molybdenum (Mo), gold (Au), aluminum (Al), chromium (Cr), tungsten (W), and copper (Cu). Among them, in particular, molybdenum (Mo) has a smaller difference between the support substrate 100 and the coefficient of thermal expansion than other elements, and thus it is possible to prevent the occurrence of peeling due to excellent adhesion. In contrast, the back electrode layer 200 may include graphene. In more detail, the back electrode layer 200 may be formed of a graphene layer, but is not limited thereto.

The light absorption layer 300 is disposed on the rear electrode layer 200. The light absorption layer 300 includes an I-III-VI compound. For example, the light absorbing layer 300 may be formed of a copper-indium-gallium-selenide-based (Cu (In, Ga) (Se, S) ₂ ; CIGSS-based) crystal structure, copper-indium-selenide-based, or copper- It may have a gallium-selenide-based crystal structure.

The buffer layer 400 is disposed on the light absorption layer 300. The buffer layer 400 includes cadmium sulfide, ZnS, In _x S _y, and In _x Se _y Zn (O, OH). The high resistance buffer layer 500 is disposed on the buffer layer 400. The high resistance buffer layer 500 includes zinc oxide (i-ZnO) that is not doped with impurities.

The front electrode layer 600 may be disposed on the light absorbing layer 300. For example, the front electrode layer 600 may be disposed in direct contact with the high-resistance buffer layer 500 on the light absorption layer 300.

The front electrode layer 600 may include graphene. In more detail, the front electrode layer 600 may be composed of graphene. As used herein, the term "grapheme" refers to a graphene in which a plurality of carbon atoms are covalently linked to each other to form a polycyclic aromatic molecule, forming a layer or sheet form. The carbon atoms form a 6-membered ring as the basic repeating unit, but may further include a 5-membered ring and / or a 7-membered ring.

The front electrode layer 600 including the graphene has excellent electrical characteristics. That is, the front electrode layer 600 including the graphene may move electrons 100 times faster than silicon and flow about 100 times more current than copper as an excellent conductive material. Accordingly, the front electrode layer 600 including the graphene may collect more electrons formed in the light absorbing layer as compared to the front electrode layer used in the related art.

As mentioned above, due to the excellent electrical properties of graphene, the thickness of the front electrode layer 600 including the graphene may be reduced by about 50% or more than the thickness of the front electrode layer, which is conventionally used. The cell can be made thinner in thickness. For example, the thickness of the front electrode layer 600 including the graphene may be about 100 nm to about 500 nm, but is not limited thereto.

In addition, the front electrode layer 600 including the graphene has excellent mechanical strength and shielding properties of moisture (H ₂ O) or oxygen (O ₂ ). Accordingly, the front electrode layer 600 including the graphene may minimize the penetration of moisture or oxygen into the solar cell along the interface. That is, the solar cell according to the embodiment effectively contributes to securing the stability and reliability of the device by effectively protecting the solar cells from moisture and oxygen.

2 is a cross-sectional view showing a cross section of the solar cell according to the second embodiment. Referring to FIG. 2, the solar cell according to the second embodiment includes a composite front electrode layer. That is, the front electrode layer according to the second embodiment may include a metal oxide layer 610 disposed on the light absorbing layer 300 and a graphene layer 620 disposed on the metal oxide layer 610. For example, the metal oxide 610 may include zinc oxide, indium tin oxide (ITO), or indium zinc oxide (IZO). In addition, the metal oxide may include conductive impurities such as aluminum (Al), alumina (Al ₂ O ₃ ), magnesium (Mg), or gallium (Ga). In more detail, the metal oxide 610 may include aluminum doped zinc oxide (AZO) or gal doped zinc oxide (GZO), but is not limited thereto.

In addition, each of the metal oxide layer 610 and the graphene layer 620 may be formed of a single layer or a plurality of layers. For example, the front electrode layer 600 according to the second embodiment may be formed by alternately depositing a plurality of metal oxide layers 610 and a plurality of graphene layers 620, but is not limited thereto.

As mentioned above, the solar cell according to the embodiment provides a front electrode layer including graphene, thereby improving photo-electric conversion efficiency and simultaneously providing moisture (H ₂ O) or oxygen (O ₂ ). Penetration into the solar cell can be minimized. That is, the solar cell according to the embodiment effectively contributes to securing the stability and reliability of the device by effectively protecting the solar cells from moisture and oxygen.

3 to 7 are cross-sectional views illustrating a method of manufacturing the solar cell according to the second embodiment. For a description of the present manufacturing method, refer to the description of the solar cell described above.

Referring to FIG. 3, the back electrode layer 200 is formed on the support substrate 100. The back electrode layer 200 may be formed by physical vapor deposition (PVD) or plating.

Next, referring to FIG. 4, the light absorbing layer 300 is formed on the back electrode layer 200. The light absorbing layer 300 may be, for example, copper-indium-gallium-selenide-based (Cu (In, Ga) Se ₂ ; CIGS-based) while simultaneously evaporating copper, indium, gallium, and selenium. The method of forming (300) and the method of forming a metal precursor film and forming it by the selenization process are used widely.

When the metal precursor film is formed and selenization is subdivided, a metal precursor film is formed on the back electrode 300 by a sputtering process using a copper target, an indium target, and a gallium target. Thereafter, the metal precursor film is formed of a copper-indium-gallium-selenide-based (Cu (In, Ga) Se ₂ ; CIGS-based) light absorbing layer by a selenization process.

Alternatively, the copper target, the indium target, the sputtering process using the gallium target, and the selenization process may be performed simultaneously.

Alternatively, the CIS-based or CIG-based optical absorption layer 300 can be formed by using only a copper target and an indium target, or by a sputtering process and a selenization process using a copper target and a gallium target.

Subsequently, referring to FIG. 5, a buffer layer 400 and a high resistance buffer layer 500 are sequentially formed on the light absorbing layer. The buffer layer 400 may be formed by depositing cadmium sulfide on the light absorbing layer 300 by chemical bath deposition (CBD). In addition, zinc oxide is deposited on the buffer layer 400 by a sputtering process, and the high resistance buffer layer 500 is formed.

Referring to FIG. 6, a transparent conductive material is stacked on the high resistance buffer layer 500 to form a metal oxide layer 610. The metal oxide layer 610 is a window layer which forms a pn junction with the light absorbing layer 300 together with the graphene layer 620. It may be formed of zinc oxide (ZnO) having good electrical conductivity.

In this case, the metal oxide layer 610 having a low resistance value may be formed by doping aluminum with zinc oxide. For example, the metal oxide layer 610 may be formed by depositing using a ZnO target by RF sputtering, reactive sputtering using a Zn target, and organometallic chemical vapor deposition.

In addition, in the case of manufacturing the front electrode layer 600 including only graphene, the process of forming the metal oxide layer 610 may be omitted.

Referring to FIG. 7, a graphene layer 620 is formed on the metal oxide layer 610. The graphene layer 620 may be formed by directly transferring the graphene layer grown on the metal oxide layer 610 or grown on another substrate.

For example, the graphene layer 620 may be manufactured by coating a graphene oxide solution on the high resistance buffer layer 500 and heat treating the graphene oxide solution. The graphene oxide solution may include a carbon nanocomposite including graphene, a dispersion solvent, a surfactant, a binder, and the like. Subsequently, the graphene oxide solution may be coated on the high resistance buffer layer 500 by various methods. For example, the coating method may include at least one of spin coating, Langmuir-Blocking, dip coating, spray coating, or drop coating. Thereafter, the graphene oxide solution may be dried at about 80 ° C. for about 1 hour, and then heat treated at about 350 ° C. for about 30 minutes, but the graphene layer 620 may be manufactured, but is not limited thereto.

Alternatively, the graphene layer 620 may be manufactured by the following method. First, graphite is added to sulfuric acid, and potassium permanganate is slowly added. After raising the temperature to 35 ° C., a Teflon-coated bar magnet is added and stirred for about 2 hours. After that, add a sufficient amount of water and add hydrogen peroxide until no gas is generated. After that, the graphite oxide is filtered through a glass filter, and then dried under vacuum at room temperature for about 12 hours or more. The graphene layer may be formed by adding the appropriate amount of water to use the dried graphite oxide to peel off the graphite oxide through sonication treatment. The longer the sonication time, the smaller the size of the formed graphene oxide sheets. Alternatively, in order to control the size of the graphene layer may be slowly peeled off by stirring with a Teflon coated bar magnet.

Alternatively, the graphene layer 620 may be formed by growing a graphene layer on another substrate and transferring the grown graphene layer.

In one embodiment, first, a substrate including a metal catalyst layer is prepared. The metal catalyst layer is Ni, Co, Fe, Pt, Au, Al, Cr, Cu, Mg, Mn, Mo, Rh, Si, Ta, Ti, W, U, V, Zr, brass (brass), bronze ( but may include, but is not limited to, one or more metals or alloys selected from the group consisting of bronze, white brass, stainless steel, and Ge. In addition, the metal catalyst layer may be in the form of a thin film, but is not limited thereto.

Subsequently, the graphene layer is formed by providing a reaction gas and a heat including a carbon source on the substrate including the metal catalyst layer. For example, the graphene layer may be formed on the metal catalyst layer by chemical vapor deposition.

Subsequently, the substrate on which the graphene layer is formed is impregnated in an etching solution and the metal catalyst layer is removed to separate the substrate and the graphene sheet. The etching solution may be a solution containing ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ , HF, BOE, Fe (NO ₃ ) ₃ , or iron chloride (Iron (III) Chloride, FeCl ₃ ), It is not limited to this. In addition to the above-mentioned etching method, the substrate may be removed by reactive ion etching, ion milling, ashing, and the like.

Finally, the separated graphene layer may be transferred onto the high resistance buffer layer 500 by various transfer methods, for example, a roll-to-roll process, a dry process, or a wet process.

Features, structures, effects, and the like described in the above embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects, and the like illustrated in the embodiments may be combined or modified with respect to other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of illustration, It can be seen that various modifications and applications are possible. For example, each component specifically shown in the embodiments can be modified and implemented. It is to be understood that all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (9)

A rear electrode layer disposed on the supporting substrate;
A light absorbing layer disposed on the rear electrode layer; And
A solar cell disposed on the light absorbing layer and including a front electrode layer including graphene.
The method of claim 1,
The front electrode layer,
A metal oxide layer disposed on the light absorbing layer; And
A solar cell comprising a graphene layer disposed on the metal oxide layer.
3. The method of claim 2,
The front electrode layer includes a plurality of metal oxide layers and a plurality of graphene layers,
The plurality of metal oxide layers and the plurality of graphene layers are alternately deposited.
The method of claim 1,
The front electrode layer has a thickness of 100 nm to 500 nm.
The method of claim 1,
The back electrode layer is a solar cell comprising graphene.
Forming a back electrode layer on the support substrate;
Forming a light absorbing layer on the back electrode layer; And
Forming a front electrode layer comprising a graphene on the light absorbing layer comprising a solar cell manufacturing method.
The method according to claim 6,
Forming the front electrode layer including the graphene,
Providing a reaction gas comprising a carbon source and heat on a substrate including a metal catalyst layer to form a graphene layer;
Removing the metal catalyst layer layer to separate the substrate and the graphene layer; And
The method of manufacturing a solar cell comprising the step of transferring the separated graphene layer on the light absorbing layer.
The method according to claim 6,
Forming the front electrode layer including the graphene,
Coating a graphene oxide solution on the light absorbing layer,
Method for manufacturing a solar cell comprising the step of heat-treating the graphene oxide solution.
The method of claim 8,
The graphene oxide solution is a method of manufacturing a solar cell is coated on the light absorbing layer by at least one method of spin coating, Langmuir-Blocking method, dip coating, spray coating, or drop coating.

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