KR20130059227A - Solar cell and method of fabricating the same - Google Patents

Abstract

PURPOSE: A solar cell and a method for fabricating the same are provided to control the composition ratio of gallium included in a light absorption layer and improve the efficiency of a solar cell. CONSTITUTION: A back electrode layer(200) is positioned on a support substrate(100). A light absorption layer(300) is positioned on the back electrode layer. A light absorption layer includes an I-III-VI group compound. A buffer layer(400) is positioned on the light absorption layer. A front electrode layer(600) is positioned on the buffer layer.

Description

SOLAR CELL AND METHOD OF FABRICATING THE SAME

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

The energy band gap directly correlated with the efficiency of the thin-film solar cell depends on the composition ratio of the CIGS compound forming the light absorption layer, that is, the composition ratio of indium (In) and gallium (Ga) in CuIn1-xGaxSe2. The energy band gap between eV was obtained. At present, the CIGS light absorption layer 30 of the solar cell having the highest efficiency has an energy band gap of approximately 1.2 eV, and the composition ratio of the CIGS compound at this time is known as CuIn0.74Ga0.26Se2.

However, in the conventional CIGS-based thin film solar cell, the CIGS-based compound is a quaternary compound, and when manufacturing a light absorbing layer using the same, there are many difficulties in the composition and process control, and in the case of the conventional CIGS-based thin film solar cell Since the light absorbing layer 30 having a single energy bandgap is used, a wavelength other than the energy bandgap corresponding thereto is passed through as it is, so that there is a problem in that a large portion of solar loss occurs.

Therefore, there is an urgent need to develop a thin-film solar cell having higher efficiency than the conventional CIGS-based thin-film solar cell and having simpler and easier composition and process control. In particular, when manufacturing such a solar cell, it is possible to adjust the energy band gap by grading the composition ratio of gallium included in the light absorbing layer, there is a problem that it is difficult to grade the composition ratio of gallium by the conventional heat treatment method.

Embodiments provide a solar cell having improved efficiency.

Solar cell according to the embodiment, the support substrate; A back electrode layer on the support substrate; A light absorbing layer on the back electrode layer; A buffer layer on the light absorbing layer; And a front electrode layer disposed on the buffer layer, wherein the amount of crystallization included in the light absorbing layer is different from each other.

A method of manufacturing a solar cell according to an embodiment includes forming a back electrode layer on a support substrate; And forming a precursor of a light absorbing layer on the back electrode layer, wherein the precursor includes an upper surface and a lower surface opposite to each other, and the forming of the precursor comprises irradiating a laser onto the upper surface and the lower surface. It includes a step.

The solar cell according to the embodiment has different amounts of crystallization included in the light absorbing layer. Specifically, the energy band gap of the light absorbing layer may be adjusted by grading the composition ratio of gallium included in the light absorbing layer, thereby improving efficiency of the solar cell. That is, it is possible to provide a high efficiency solar cell by adjusting the internal composition ratio of the solar cell.

The method of manufacturing a solar cell according to the embodiment includes irradiating a laser. In the irradiating of the laser, a local laser may be irradiated to the precursor of the light absorbing layer. Through this, the composition ratio of gallium included in the light absorbing layer can be adjusted by controlling the diffusion of gallium. Through this, the energy band gap of the light absorbing layer may be adjusted, and further, the efficiency of the solar cell may be improved.

1 is a cross-sectional view showing a cross section of a solar cell according to an embodiment.
2 is a schematic view showing a light absorbing layer included in the solar cell according to the embodiment.
3 is a cross-sectional view illustrating a method of manufacturing a solar cell according to an embodiment.

In the description of embodiments, each layer, region, pattern, or structure may be “on” or “under” the substrate, each layer, region, pad, or pattern. Substrate formed in ”includes all formed directly or through another layer. Criteria for the top / bottom or bottom / bottom of each layer will be described with reference to the drawings.

The thickness or the size of each layer (film), region, pattern or structure in the drawings may be modified for clarity and convenience of explanation, and thus does not entirely reflect the actual size.

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

1 and 2, a solar cell according to an embodiment will be described in detail. 1 is a cross-sectional view showing a cross section of a solar cell according to an embodiment. 2 is a schematic view showing a light absorbing layer included in the solar cell according to the embodiment.

1 and 2, the solar cell includes a support substrate 100, a back electrode layer 200, a light absorbing layer 300, a buffer layer 400, a high resistance buffer layer 500, and a front electrode layer 600. .

The supporting substrate 100 has a plate shape and supports the rear electrode layer 200, the light absorbing layer 300, the buffer layer 400, the high resistance buffer layer 500, and the front electrode layer 600.

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 supporting substrate 100 may be transparent. The support substrate 100 may be rigid or flexible.

The back electrode layer 200 is disposed on an upper surface of the support substrate 100. The back electrode layer 200 is a conductive layer. Examples of the material used as the back electrode layer 200 may include a metal such as molybdenum (Mo).

In addition, the back electrode layer 200 may include two or more layers. In this case, each of the layers may be formed of the same metal, or may be formed of different metals.

The light absorbing layer 300 is disposed on the back electrode layer 200. The light absorbing layer 300 includes a group 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 2; CIGS-based) crystal structure, copper-indium-selenide-based, or copper-gallium-selenide-based. It may have a crystal structure.

The amount of crystallization included in the light absorbing layer 300 may be different. The amount may be a composition ratio of a material included in the light absorbing layer 300. The amount may be a concentration of a material included in the light absorbing layer 300. The amount may be a content of a material included in the light absorbing layer 300. Here, the material may include gallium (Ga).

Specifically, the light absorbing layer 300 includes Cu (In1-xGax) Se2, and x may be changed. Specifically, x becomes smaller from the upper surface 302 of the light absorbing layer 300 to the central portion 300a of the light absorbing layer 300, and the light absorbing layer (from the lower surface 301 of the light absorbing layer 300). It may become smaller toward the central portion 300a of the 300. That is, the composition ratio of gallium included in the light absorbing layer 300 may vary.

Here, the range of x is as follows.

Equation

0 <x <1

The energy band gap of the light absorption layer 300 may be about 1 eV to 1.8 eV.

The energy band gap of the light absorbing layer 300 may be adjusted by grading the composition ratio of gallium, thereby improving efficiency of the solar cell. That is, it is possible to provide a high efficiency solar cell by adjusting the internal composition ratio of the solar cell.

The buffer layer 400 is disposed on the light absorbing layer 300. The buffer layer 400 is in direct contact with the light absorbing layer 300. The buffer layer 400 may include a sulfide. For example, the buffer layer 400 may include cadmium sulfide (CdS).

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 energy band gap of the high resistance buffer layer 500 may be about 3.1 eV to 3.3 eV.

The front electrode layer 600 is disposed on the light absorbing layer 300. In more detail, the front electrode layer 600 is disposed on the high resistance buffer layer 500.

The front electrode layer 600 is disposed on the high-resistance buffer layer 500. The front electrode layer 600 is transparent. Examples of the material used as the front electrode layer 600 include aluminum doped ZnO (AZO), indium zinc oxide (IZO), indium tin oxide (ITO), and the like. Can be.

The front electrode layer 600 may have a thickness of about 500 nm to about 1.5 μm. In addition, when the front electrode layer 600 is formed of zinc oxide doped with aluminum, aluminum may be doped at a ratio of about 2.5 wt% to about 3.5 wt%. The front electrode layer 600 is a conductive layer.

Hereinafter, a manufacturing method of a solar cell according to an embodiment will be described with reference to FIG. 3. For the sake of clarity and simplicity, detailed description of parts identical or similar to those described above will be omitted.

3 is a cross-sectional view illustrating a method of manufacturing a solar cell according to an embodiment.

First, a metal such as molybdenum is deposited on the support substrate 100 by a sputtering process, and the back electrode layer 200 is formed. The rear electrode layer 200 may be formed by two processes having different process conditions.

An additional layer such as a diffusion barrier may be interposed between the support substrate 100 and the back electrode layer 200.

Subsequently, the precursor 320 of the light absorbing layer 300 is formed on the back electrode layer 200. The precursor 320 of the light absorbing layer 300 may be formed by a sputtering process or an evaporation method.

The precursor 320 of the light absorbing layer 300 may be formed by, for example, a stacked precursor 320 film having a predetermined composition ratio consisting of a copper-gallium alloy layer and an indium layer. It may also be formed by a sputtering process using a copper target, an indium target, and a gallium target. Therefore, the precursor 320 of the light absorbing layer 300 may be formed of constituent elements of copper, indium, and gallium.

Subsequently, the metal precursor 320 layer 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. Here, the selenization process refers to a process of heat treatment at low temperature in an atmosphere made of selenium and / or sulfur-containing gas.

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.

After forming the precursor 320, the laser irradiation step. In the step of irradiating the laser may be diffusion of the gallium.

 In the step of irradiating the laser, a local laser may be irradiated to the precursor 320 of the light absorbing layer 300.

The irradiating the laser may irradiate a laser to the upper surface 322 and the lower surface 321 of the precursor 320, respectively.

Specifically, the step of irradiating the laser includes the step of irradiating the first laser (L1) and the step of irradiating the second laser (L2).

In the irradiating of the first laser L1, the first laser L1 may be irradiated onto the upper surface 322. In the irradiating of the second laser L2, the second laser L2 may be irradiated onto the lower surface 321.

The energy density of the first laser L1 and the second laser L2 may be provided differently. Since the energy densities of the first laser L1 and the second laser L2 are different from each other, the diffusion rate of the gallium included in the precursor 320 may be adjusted. Through this, the composition ratio of the gallium may vary.

The composition ratio of the gallium is lowered from the upper surface 322 of the precursor 320 toward the central portion 320a of the precursor 320, and the precursor 320 at the lower surface 321 of the precursor 320. It can be lowered toward the central portion (320a).

That is, the composition ratio of gallium included in the light absorbing layer 300 may be controlled by controlling the diffusion of gallium. Through this, the energy band gap of the light absorbing layer 300 can be adjusted, and further, the efficiency of the solar cell can be improved.

Subsequently, although not illustrated, zinc oxide may be deposited on the buffer layer 400 by a sputtering process, and the high resistance buffer layer 500 may be formed.

In addition, the front electrode layer 600 is formed on the high resistance buffer layer 500. In order to form the front electrode layer 600, a transparent conductive material is stacked on the high resistance buffer layer 500. Examples of the transparent conductive material include aluminum doped zinc oxide and the like.

The features, structures, effects and the like described in the foregoing embodiments are included in at least one embodiment of the present invention and are not necessarily limited to one embodiment. In addition, 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 construed as limiting the scope of the present invention. It can be seen that various modifications and applications are possible. For example, each component specifically shown in the embodiments may be modified. It is to be understood that the present invention may be embodied in many other specific forms without departing from the spirit or essential characteristics thereof.

Claims (14)

Support substrate;
A back electrode layer on the support substrate;
A light absorbing layer on the back electrode layer;
A buffer layer on the light absorbing layer; And
A front electrode layer on the buffer layer;
A solar cell having a different amount of crystallization included in the light absorbing layer. The method of claim 1,
The amount is a solar cell of the composition ratio of the material contained in the light absorbing layer. The method of claim 1,
The amount is the concentration of the material contained in the light absorbing layer solar cell. The method of claim 1,
The amount is the amount of material contained in the light absorbing layer solar cell. The method according to any one of claims 2 to 4,
The material includes a gallium (Ga). The method of claim 1,
The light absorbing layer is a solar cell containing Cu (In1-xGax) Se2. The method according to claim 6,
X is smaller toward the center of the light absorbing layer from the upper surface of the light absorbing layer, and smaller toward the center of the light absorbing layer from the lower surface of the light absorbing layer. Forming a back electrode layer on the support substrate; And
Forming a precursor of a light absorbing layer on the back electrode layer;
The precursor includes an upper surface and a lower surface opposite to each other,
And irradiating a laser to the upper surface and the lower surface after the forming of the precursor. 9. The method of claim 8,
The irradiating the laser may include irradiating a first laser to the upper surface and irradiating a second laser to the lower surface. 10. The method of claim 9,
The method of manufacturing a solar cell having different energy densities of the first laser and the second laser. 9. The method of claim 8,
The precursor method of manufacturing a solar cell comprising gallium (Ga). The method of claim 11,
The method of manufacturing a solar cell is a diffusion of the gallium in the step of irradiating the laser. The method of claim 11,
The method of manufacturing a solar cell in which the composition ratio of the gallium is different in the step of irradiating the laser. The method of claim 13,
The composition ratio of the gallium is lowered toward the center of the precursor from the upper surface of the precursor, and lowered toward the center of the precursor from the lower surface of the precursor.

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