KR101081079B1 - Solar cell and method of fabricating the same - Google Patents

Abstract

Solar cell according to the embodiment, the substrate; A back electrode layer formed on the substrate; A light absorbing layer formed on the substrate, the light absorbing layer having a distribution in which a composition of a group VI element is increased toward a central region in a vertical direction; A buffer layer formed on the light absorbing layer; And it includes a front electrode layer formed on the buffer layer, it is possible to improve the efficiency by controlling the composition distribution of the CIGS constituting the light absorbing layer.

Solar cell, CIGS layer

Description

SOLAR CELL AND METHOD OF FABRICATING THE SAME

Embodiments relate to solar cells.

Recently, as the demand for energy increases, development of solar cells for converting solar energy into electrical energy is in progress.

In particular, a CIGS solar cell which is a pn heterojunction device having a substrate structure including a glass substrate, a metal back electrode layer, a p-type CIGS-based light absorbing layer, a high resistance buffer layer, an n-type window layer, and the like is widely used.

Photovoltaic (PV) manufacturing methods use vacuum co-evaporation and selenization at high temperatures.

Since the selenization process is performed after the vacuum deposition process, control of a depth profile for Cu, In, and Ga is required.

In addition, in order to increase the efficiency of the battery, a high temperature (for example, 500 ~ 600 ° C or more) process for the photocell should be performed as a post-treatment process. Therefore, the kind of substrate used can be restricted.

The embodiment provides a solar cell and a method of manufacturing the same, by adjusting a depth profile of the CIGS light absorbing layer to improve light efficiency.

Solar cell according to the embodiment, the substrate; A back electrode layer formed on the substrate; A light absorbing layer formed on the substrate, the light absorbing layer having a distribution in which a composition of a group VI element is increased toward a central region in a vertical direction; A buffer layer formed on the light absorbing layer; And a front electrode layer formed on the buffer layer.

A method of manufacturing a solar cell according to an embodiment includes forming a back electrode layer on a substrate; Forming at least one multilayer on the back electrode layer including a group I element layer, a group III element layer, and a group VI element layer; Performing an electron beam treatment on the multilayer to form a light absorbing layer having a distribution in which a composition of the group VI element layer is increased toward a central region based on a vertical direction; And forming a front electrode layer on the light absorbing layer.

According to the embodiment, the light efficiency of the light absorbing layer including the Group I-Group III-VI compound of the solar cell can be adjusted to improve the light efficiency.

The distribution of group VI elements in the light absorbing layer may be controlled to increase toward the center region. In addition, the band gap of the light absorbing layer may be adjusted by controlling the composition distribution of the group III element to be increased as the rear electrode layer approaches the rear electrode layer.

Accordingly, the electron velocity of the light absorbing layer can be improved, and the decrease in efficiency can be minimized.

The light absorbing layer may be formed by a low temperature process.

Accordingly, it is possible to use a variety of substrates, it is possible to reduce the cost.

The light absorbing layer may be formed through electron beam treatment after forming a multilayer including a group I-III-VI group compound in one chamber.

Accordingly, the grain size of the light absorbing layer can be greatly grown, and the conductivity can be increased.

In addition, since multiple layers are formed in one chamber, the selenization process may be omitted.

Therefore, the manufacturing process of the solar cell can be simplified.

In addition, the group VI-based element layer of the multi-layered element layer may have a sandwich structure, thereby reducing selenium consumption and simplifying the process.

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" formed through 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 description, and does not mean a size that is actually applied.

1 to 6 are cross-sectional views illustrating a method of manufacturing a solar cell according to an embodiment.

Referring to FIG. 1, a back electrode layer 200 is formed on a substrate.

The substrate 100 may be glass, and a ceramic substrate, a metal substrate, or a polymer substrate may also be used.

For example, soda lime glass or high strained point soda glass may be used as the glass substrate.

As the metal substrate, a substrate including stainless steel or titanium may be used.

Polymer substrates include transparent plastics such as polyimide, polyethylene terephthalate (PET), polyethylene naphathalate (PEN), polycarbonate, polystyrene, and polypropylene (plastic) substrates may be used.

The substrate 100 may be an insulator and may be rigid or flexible.

In particular, since the CIGS layer formed on the substrate 100 may be formed through a low temperature deposition process, various types of substrates may be used.

The back electrode layer 200 may be formed of a conductor such as metal.

The back electrode layer 200 may be formed of a metal to improve series resistance and to increase electrical conductivity.

For example, the back electrode layer 200 may be formed by a sputtering process using molybdenum (Mo) as a target.

This is due to the high conductivity of molybdenum (Mo) and ohmic bonding with the light absorbing layer.

The molybdenum thin film as the back electrode layer 200 should have a low specific resistance as an electrode, and have excellent adhesion to the substrate 100 so that peeling does not occur due to a difference in thermal expansion coefficient.

The material forming the back electrode layer 200 is not limited thereto, and may be formed of molybdenum (Mo) doped with indium tin oxide (ITO) or sodium (Na) ions.

Although not shown in the drawing, the back electrode layer 200 may be formed of at least one layer. In addition, when the back electrode layer 200 is formed of a plurality of layers, the layers constituting the back electrode layer may be formed of different materials.

Referring to FIG. 2, a CIGS-based light absorbing layer 300 is formed on the back electrode layer 200.

The light absorbing layer 300 includes an Ib-IIIb-VIb-based compound.

In more detail, the light absorbing layer 300 includes a copper-indium-gallium-selenide-based Cu (In _1-x Ga _x ) Se ₂ compound or a copper-indium-selenide-based (CuInSe ₂ ) compound. Here, x may be greater than 0 and less than 1.

That is, the light absorbing layer 300 may have a copper-indium-gallium-selenide-based crystal structure or a copper-indium-selenide-based crystal structure.

The composition of each component of the light absorbing layer 300 may vary depending on the location. The composition of the Group I-Group III-VI compound may vary depending on the depth of the light absorbing layer 300.

That is, a desired unit element film, for example, a Ga film, a Cu film, a Se film, an In film, or a compound film in which two or more elements are combined in the light absorbing layer 300 may be artificially disposed.

Thus, a depth profile of the light absorbing layer 300 may be optimized to improve light efficiency.

3A, 3B, and 4 are graphs showing composition distributions according to depths of the light absorbing layer 300.

As shown in FIG. 3A, selenium, which is a group VI element, may be formed such that its composition becomes higher toward the central region of the light absorbing layer 300.

Alternatively, as illustrated in FIG. 3B, selenium, which is a group VI element, may be formed to have a composition having a step inside the light absorbing layer 300.

As shown in FIG. 4, the closer to the back electrode layer 200, the greater the composition ratio of gallium (Ga) of the light absorbing layer 300.

Accordingly, the band gap energy of the light absorbing layer 300 is increased, and the mobility of electrons can be improved.

In addition, the closer to the CIGS layer surface area, the lower the composition ratio of copper (Cu) of the light absorbing layer 300. As a result, the p-type impurity of the light absorbing layer 300 may be low in concentration, thereby improving junction properties.

The light absorbing layer 300 performs a sputtering process using various combinations of targets in one chamber, and forms a multilayer composed of each unit element.

The CIGS (Cu (InGa) Se ₂ ) light absorbing layer 300 may be formed through the electron beam assisted sputtering process for the multilayer.

In particular, the sputtering process may be formed by a low temperature process of 100 ~ 200 ℃, it is possible to use a variety of substrates that are not limited by the temperature.

In addition, the size of the grains of the grains constituting the light absorbing layer 300 may be greatly increased through the electron beam treatment of the multilayer, and the conductivity may be improved.

A method for adjusting the depth profile of the light absorbing layer 300 as described above will be described with reference to FIGS. 5A to 5F.

The light absorbing layer 300 may be formed through sputtering or co-evaporation proceeding at a low temperature of 100 to 200 ° C.

Referring to FIG. 5A, a unit element film, or a binary or ternary compound film is artificially controlled and stacked on a layer-by-layer layer on the rear electrode layer 200.

For example, a first CuGa layer 311, a first In layer 312, a Se layer 313, and a second CuGa on the back electrode layer 200 in a chamber (not shown) at a temperature of 100 to 200 ° C. A multilayer 310 comprising a layer 314 and a second In layer 315 is stacked.

The first CuGa layer 311 is 0.7 μm, the first In layer 312 is 0.3 μm, the Se layer 313 is 0.1-0.5 μm, the second CuGa layer 314 is 0.7 μm, and the second In layer ( 315) may be formed to a thickness of 0.3㎛. Here, the error range of each layer may be about ± 0.3㎛.

Meanwhile, the composition ratio of Cu and Ga in the first CuGa layer 311 may be 6: 4. In addition, the composition ratio of Cu and Ga in the second CuGa layer 314 may be 7: 3.

As such, in the case of the compound layer, the depth profile in the CIGS light absorbing layer 300 may be controlled by artificially adjusting the respective composition ratio.

In detail, a sputtering process using a CuGa target, an In target, and a Se target is performed in one sputtering chamber, and thus, the first CuGa layer 311, the first In layer 312, and the Se are sequentially formed on the back electrode layer 200. The layer 313, the second CuGa layer 314, and the second In layer 315 may be formed.

That is, the unit layers constituting the CIGS layer may be formed as a multi-layer 310 by one chamber. In particular, the Se layer 313 may have a sandwich structure interposed between the first In layer 312 and the second CuGa layer layer 314.

Accordingly, the additional selenization process can be omitted to simplify the process.

That is, in general, when forming the light absorbing layer, the selenization process after the CIG formation is carried out after moving to a separate chamber, so the selenium (Se) consumption was increased.

In an embodiment, the first CuGa layer 311, the first In layer 312, the Se layer 313, the second CuGa layer 314, and the second In layer 315 are formed by one sputtering process. This can simplify the process.

In addition, the Se layer 313 has a sandwich structure interposed between other layers, thereby simplifying the process while reducing selenium consumption.

Accordingly, the composition ratio may be controlled by artificially adjusting the depth profile of each unit film.

Next, the first CuGa layer 311, the first In layer 312, the Se layer 313, the second CuGa layer 314, and the second In layer 315 are formed on the back electrode layer 200. After that, an electron beam process is performed, and the light absorbing layer 300 is formed.

The electron beam (e-) treatment process may form a CIGS image and grow crystal grains by irradiating an electron beam onto the multilayer layer 310.

For example, the electron beam (e-) treatment process may apply energy of 2 to 5 keV, and may proceed for 1 to 30 minutes.

The grain size of the light absorbing layer 300 may be grown to 1 to 5 μm through the electron beam (e−) treatment process. In addition, the carrier concentration of the light absorbing layer 300 may have a 1.0 × 10 ¹⁴ ~ 1.0 × 10 ¹⁶ atoms / cm 3.

Accordingly, the conductivity of the light absorbing layer 300 may be improved.

Meanwhile, the first CuGa layer 311, the first In layer 312, the Se layer 313, the second CuGa layer 314, and the second In layer 315 are co-evaporated. It may be formed.

For example, a CuGa source, an In source, and a Se source are used and co-deposition is performed at a low temperature, thereby forming a first CuGa layer 311, a first In layer 312, a Se layer 313, and a first CuGa layer on the back electrode layer. 2 CuGa layer 314 and the second In layer 315 are formed.

Thereafter, the electron beam treatment process may be performed to form the CIGS light absorbing layer 300 as illustrated in FIG. 2.

5B, 5C, 5D, 5E, and 5F are cross-sectional views illustrating various structures of each unit film forming the light absorbing layer 300. On the other hand, the structure of the unit film is not limited to this embodiment may be laminated in various forms. 5B, 5C, 5D, 5E, and 5F, the method of forming each layer and the light absorbing layer forming process are the same as those of FIG. 4A, and thus detailed descriptions thereof will be omitted.

Referring to FIG. 5B, a multilayer 320 including a CuGa layer 321, a first In layer 322, a Se layer 323, and a second In layer 324 on the back electrode layer 200. This is laminated.

That is, a sputtering process using a CuGa target, an In target, and a Se target is performed to sequentially the CuGa layer 321, the first In layer 322, the Se layer 323, and the second on the back electrode layer 200. In layer 324 may be formed.

Thereafter, an electron beam (E-beam) treatment process may be performed on the multilayer 320 to form the light absorbing layer 300.

Referring to FIG. 5C, a multilayer 330 including a Ga layer 331, an In layer 332, an Se layer 333, and a Cu layer 334 is stacked on the back electrode layer 200. In addition, the CIGS-based light absorbing layer 300 may be formed by an electron beam treatment process.

Referring to FIG. 5D, a first Ga layer 341, a first In layer 342, a first Se layer 343, a first Cu layer 344, and a second Ga layer are formed on the back electrode layer 200. A multilayer 340 including 345, a second In layer 346, a second Se layer 347, and a second Cu layer 348 is stacked. The CIGS light absorbing layer 300 may be formed by an electron beam treatment process.

Referring to FIG. 5E, a multilayer 350 including a CuInGa layer 351, a CuInGaSe layer 352, and a CuInGa layer 353 is stacked on the back electrode layer 200. That is, each unit film of the multi-layer 350 may be formed of a ternary or more compound.

Thereafter, the CIGS-based light absorbing layer 300 may be formed by an electron beam treatment process.

Referring to FIG. 5F, a multilayer 360 including a CuGa layer 361, an InSe layer 362, and a CuGaSe layer 343 is stacked on the back electrode layer 200. The CIGS light absorbing layer 340 may be formed by an electron beam treatment process.

As described above, various kinds of multi-layers 310, 320, 330, 340, 350 and 360 are formed on the back electrode layer 200 through sputtering or co-deposition through a single process, and the CIGS light absorbing layer 300 is formed through an electron beam treatment process. can do.

Referring to FIG. 6, a buffer layer 400 and a high resistance buffer layer 500 are formed on the light absorbing layer 300.

The buffer layer 400 may be formed of at least one or more layers on the light absorbing layer 300, and may be formed by stacking cadmium sulfide (CdS).

In this case, the buffer layer 400 is an n-type semiconductor layer, the light absorbing layer 300 is a p-type semiconductor layer. Therefore, the light absorbing layer 300 and the buffer layer 400 may form a pn junction.

The buffer layer 400 may be sputtered with zinc oxide (ZnO) as a target, and a zinc oxide layer may be further formed on the cadmium sulfide (CdS).

The high resistance buffer layer 500 may be formed as a transparent electrode layer on the buffer layer 400.

For example, the high resistance buffer layer 500 may be formed of any one of ITO, ZnO, and i-ZnO.

The buffer layer 400 and the high resistance buffer layer 500 are disposed between the light absorbing layer 300 and the front electrode to be formed later.

That is, since the difference between the lattice constant and the energy band gap between the light absorbing layer 300 and the front electrode is large, the buffer layer 400 and the high resistance buffer layer 500 having a band gap in between the two materials are inserted into a good one. A junction can be formed.

Although two buffer layers 400 are formed on the light absorbing layer 300 in the embodiment, the present invention is not limited thereto, and the buffer layer may be formed of only one layer.

Referring to FIG. 7, a transparent conductive material is stacked on the high resistance buffer layer 500 to form a front electrode layer 600.

The front electrode layer 600 may be formed of zinc oxide or indium tin oxide (ITO) including impurities such as aluminum (Al), alumina (Al 2 O 3), magnesium (Mg), and gallium (Ga).

For example, the front electrode layer 600 is a window layer forming a pn junction with the light absorbing layer 300. Since the front electrode layer functions as a transparent electrode on the front of a solar cell, zinc oxide having high light transmittance and high electrical conductivity is provided. It is formed of (ZnO).

Although described above with reference to the embodiment is only an example and is not intended to limit the invention, those of ordinary skill in the art to which the present invention does not exemplify the above within the scope not departing from the essential characteristics of this embodiment It will be appreciated that many variations and applications are possible. For example, each component specifically shown in the embodiment can be modified. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

1 to 7 are views illustrating a manufacturing process of a solar cell according to an embodiment.

Claims (8)

Board; A back electrode layer formed on the substrate; A light absorbing layer formed on the substrate, the light absorbing layer formed to have a section in which the concentration of selenium increases and then decreases toward the upper side in the vertical direction in the rear electrode layer; A buffer layer formed on the light absorbing layer; And Solar cell comprising a front electrode layer formed on the buffer layer. delete The method of claim 1, The light absorbing layer is a solar cell comprising a copper (Cu)-indium (In)-gallium (Ga)-selenide (Se) compound. delete Forming a back electrode layer on the substrate; Forming at least one or more multilayers including at least one of copper, indium, gallium, and selenium on the back electrode layer;  Performing an electron beam treatment on the multilayer to form a light absorbing layer having a distribution in which the composition of the selenium increases toward the center region in the vertical direction; And Forming a front electrode layer on the light absorbing layer; The multi-layer is a method of manufacturing a solar cell is formed so that the layer containing the selenium is interposed between the layer containing at least one of the copper, indium and gallium. delete The method of claim 5, Forming the multi layer, Forming a first element layer including at least one of copper, indium, and gallium on the back electrode layer; Forming a second element layer including selenium on the first element layer; And Forming a third element layer comprising at least one of copper, indium, and gallium on the second element layer, The multilayer is formed of a Ga film, a Cu film, a Se film, an In film or two or more elements, a compound film in which three or more elements are combined. The method of claim 5, The grain (grain) of the light absorbing layer by the electron beam treatment grows to 1 ~ 5㎛.

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