KR101305603B1 - Solar cell apparatus and method of fabricating the same - Google Patents

Abstract

Solar cell according to an embodiment of the present invention; A back electrode layer formed on the support substrate; A light absorbing layer formed on the back electrode layer; A buffer layer formed on the light absorbing layer and doped with a metal material; And a window layer formed on the buffer layer.

Description

SOLAR CELL AND MANUFACTURING METHOD THEREOF {SOLAR CELL APPARATUS AND METHOD OF FABRICATING THE SAME}

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

Solar cells (Solar Cells or Photovoltaic Cells) are the key elements of photovoltaic power generation that convert sunlight directly into electricity.

For example, when solar light having energy greater than the band-gap energy (Eg) is incident on a solar cell made of a pn junction of a semiconductor, electron-hole pairs are generated, and these electron-holes form an electric field formed at a pn junction. As a result, electrons are gathered into the n-layer and holes are gathered into the p-layer, whereby electromotive force (photovoltage) is generated between pn. At this time, when the load is connected to the electrodes at both ends, current flows.

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

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

In such a solar cell, research is being conducted to improve electrical properties such as low resistance and high transmittance and to improve productivity.

The high resistance buffer layer has a band gap between the p-type CIGS-based light absorbing layer and the n-type window layer, and is generally used because of its excellent electrical properties. However, the band gap is relatively fixed, so that the buffer layer has a wide range of band gaps. In forming this, there is room for improvement.

The solar cell according to the embodiment of the present invention may form a buffer layer having a wide band gap by adjusting the band gap. Accordingly, the photoelectric conversion efficiency of the solar cell can be improved.

In addition, when the buffer layer is formed by using an evaporation process, the light absorbing layer may be continuously processed, and thus productivity may be improved.

Solar cell according to an embodiment of the present invention; A back electrode layer formed on the support substrate; A light absorbing layer formed on the back electrode layer; A buffer layer formed on the light absorbing layer and doped with a metal material; And a window layer formed on the buffer layer.

The solar cell according to the embodiment of the present invention may form a buffer layer having a wide band gap by adjusting the band gap. Accordingly, the photoelectric conversion efficiency of the solar cell can be improved.

In addition, when the buffer layer is formed by using an evaporation process, the light absorbing layer may be continuously processed, and thus productivity may be improved.

1 is a cross-sectional view showing a solar cell according to an embodiment.
2 to 5 are views illustrating a process of manufacturing the solar cell panel according to the 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.

1 is a cross-sectional view showing a solar cell according to an embodiment. Referring to FIG. 1, the solar cell panel 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 window layer 600.

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

The support substrate 100 may be an insulator. The support substrate 100 may be a glass substrate, a plastic substrate such as a polymer, or a metal substrate. In addition, a ceramic substrate such as alumina, stainless steel, a flexible polymer, or the like may be used as the material of the support substrate 100. The support substrate 100 may be transparent, rigid, or flexible.

When soda lime glass is used as the support substrate 100, sodium (Na) contained in the soda lime glass may diffuse into the light absorbing layer 300 formed of CIGS during the manufacturing process of the solar cell, whereby the light absorbing layer The charge concentration of 300 may be increased. This may be a factor that can increase the photoelectric conversion efficiency of the solar cell.

The back electrode layer 200 is disposed on the support substrate 100. The back electrode layer 200 is a conductive layer. The back electrode layer 200 may allow electric current generated in the light absorbing layer 300 of the solar cell to move so that current flows to the outside of the solar cell. The back electrode layer 200 should have high electrical conductivity and low specific resistance in order to perform this function.

In addition, the back electrode layer 200 must maintain high temperature stability during heat treatment in a sulfur (S) or selenium (Se) atmosphere accompanying the formation of the CIGS compound. In addition, the back electrode layer 200 should be excellent in adhesion with the support substrate 100 so that the backing layer and the support substrate 100 are not peeled due to a difference in thermal expansion coefficient.

The back electrode layer 200 may be formed of any one of molybdenum (Mo), gold (Au), aluminum (Al), chromium (Cr), tungsten (W), and copper (Cu). In particular, since molybdenum (Mo) has a smaller difference between the support substrate 100 and the coefficient of thermal expansion than other elements, it is possible to prevent the occurrence of peeling phenomenon due to excellent adhesion and to the back electrode layer 200 described above. Overall required properties can be met. The back electrode layer 200 may be formed to a thickness of 400nm to 1000nm.

The light absorbing layer 300 may be formed on the back electrode layer 200. The light absorbing layer 300 includes a p-type semiconductor compound. In more detail, the light absorbing layer 300 includes a group I-III-VI compound. For example, the light absorbing layer 300 is copper-indium-gallium-selenide-based (Cu (In, Ga) Se _2; CIGS-based) crystal structure, a copper-indium-selenide-based or copper-gallium-selenide Crystal structure. The energy band gap of the light absorbing layer 300 may be about 1.1 eV to 1.2 eV, and the light absorbing layer 300 may be formed to a thickness of 1.5 μm to 2.5 μm.

The buffer layer 400 is disposed on the light absorbing layer 300. The solar cell having the CIGS compound as the light absorbing layer 300 forms a pn junction between the CIGS compound thin film as the p-type semiconductor and the window layer 600 as the n-type semiconductor. However, since the two materials have a large difference between the lattice constant and the band gap energy, a buffer layer in which a band gap is located between two materials is required in order to form a good junction.

The energy bandgap of the buffer layer 400 may be 2.2 eV to 2.5 eV. Materials for forming the buffer layer 400 include CdS, ZnS and the like, and CdS is generally used in terms of power generation efficiency of solar cells. However, a buffer layer having a bandgap having a wide range of energy bandgap is 2.4 eV. There is a problem that does not meet the demand for. In an exemplary embodiment of the present invention, the buffer layer 400 may be doped with a metal material to form a buffer layer 400 having a desired energy band gap according to the needs of the solar cell. That is, since the energy bandgap may be adjusted according to the concentration of the metal material doped in the buffer layer 400, a buffer layer having an energy bandgap suitable for the light absorbing layer 300 may be formed.

As the metal material doped in the buffer layer 400, for example, Cu may be used, and thus CuCdS may be formed. The doping concentration of Cu included in the buffer layer 400 is between 0.01 and 0.2, and the energy band gap of the buffer layer 400 may vary from 3.6 eV to 4.0 eV depending on the doping ratio. The buffer layer 400 may be formed to a thickness of 50nm to 80nm.

The high resistance buffer layer 500 may be disposed on the buffer layer 400. The high resistance buffer layer includes zinc oxide (i-ZnO) that is not doped with impurities. The energy bandgap of the high resistance buffer layer is about 3.1 eV to 3.3 eV and may be formed to a thickness of 50 nm to 60 nm.

The window layer 600 is disposed on the high resistance buffer layer 500. The window layer 600 is transparent and is a conductive layer. In addition, the resistance of the window layer 600 is higher than the resistance of the back electrode layer 200.

The window layer 600 includes an oxide. For example, the window layer 600 may include zinc oxide, indium tin oxide (ITO), or indium zinc oxide (IZO). In addition, the window layer 600 may include aluminum doped zinc oxide (AZO) or gallium doped zinc oxide (GZO). The window layer 600 may be formed to a thickness of 800nm to 1000nm.

According to the solar cell according to the embodiment of the present invention, the band gap may be adjusted to form a buffer layer having a wide band gap. Accordingly, the photoelectric conversion efficiency of the solar cell can be improved.

In addition, when the buffer layer is formed using an evaporation process, the light absorbing layer may be continuously processed, and thus productivity may be improved.

2 to 5 are cross-sectional views illustrating a method of manufacturing a solar cell according to an embodiment. For a description of the present manufacturing method, refer to the description of the solar cell described above. The description of the solar cell described above may be essentially combined with the description of the present manufacturing method.

Referring to FIG. 2, the back electrode layer 200 is formed on the support substrate 100. The back electrode layer 200 may be deposited using molybdenum. The back electrode layer 200 may be formed by a sputtering method. In addition, an additional layer such as a diffusion barrier may be interposed between the support substrate 100 and the back electrode layer 200.

Referring to FIG. 3, a light absorbing layer 300 is formed on the back electrode layer 200. For example, the light absorbing layer 300 may be formed of copper-indium-gallium-selenide (Cu (In, Ga) Se2; CIGS) while simultaneously evaporating copper, indium, gallium, and selenium. A method of forming the light absorbing layer 300 and a method of forming a metal precursor film and then forming it by a selenization process are widely used.

Alternatively, the copper target, the indium target, the sputtering process using the gallium target, and the selenization process may be performed simultaneously. In addition, a CIS-based or CIG-based light absorbing layer 300 may be formed by a sputtering process and a selenization process using only a copper target and an indium target, or using a copper target and a gallium target.

In an embodiment of the present invention, copper, indium, gallium, selenium simultaneously or separately evaporation (evaporation) while the copper-indium-gallium-selenide-based (Cu (In, Ga) Se2; CIGS-based light absorbing layer 300) Form but are not limited to this.

Referring to FIG. 4, a buffer layer 400 is formed on the light absorbing layer 300. The buffer layer 400 may include CdS, and may be formed by CBD or evaporation.

The buffer layer 400 is a method of chemical bath deposition (CBD) for 10 to 15 minutes at a temperature of 60 ℃ to 80 ℃ by mixing Thiourea (Thiourea), NH ₄ OH, Cd-salt, Cu-salt It can be formed as. The Cd-salt includes at least one of CdSO ₄ , Cd (CH ₃ COO) ₂ , CdCl ₂ , Cu-salt is CuSO ₄ , Cu (CH ₃ COO) ₂ , CuCl ₂ Or the like.

That is, Cu remaining on the surface of the light absorbing layer 300 is doped to less than 10 nm on the lower surface of the buffer layer 400. With such a configuration, Cu cannot be uniformly doped on the entire surface of the buffer layer 400. Accordingly, Cu may be doped to the entire surface of the CdS buffer layer by additionally adding Cu-salt to the CBD process when forming the buffer layer 400.

In addition, when the buffer layer 400 is formed by the evaporation method, the light absorbing layer 300 may be continuously processed after the light absorbing layer 300, and thus productivity may be improved.

Referring to FIG. 5, a high resistance buffer layer 500 is formed on the buffer layer 400. The high resistance buffer layer 500 may include zinc oxide (i-ZnO) that is not doped with impurities, and may be formed by sputtering.

Next, the window layer 600 is formed on the high resistance buffer layer 500. The window layer 600 may be formed by depositing a transparent conductive material, for example, aluminum doped zinc oxide (AZO) on the high resistance buffer layer 500 by sputtering.

The features, structures, effects and the like described in the 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 to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood 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)

Support substrate;
A back electrode layer formed on the support substrate;
A light absorbing layer formed on the back electrode layer;
A buffer layer formed on the light absorbing layer and doped with Cu; And
And a window layer formed on the buffer layer.
delete The method of claim 1,
The buffer layer is formed including CuCdS, the doping concentration of the Cu is a solar cell of 0.01 to 0.2. The method of claim 1,
The energy band gap of the buffer layer is 3.6eV to 4.0eV solar cell. The method of claim 1,
The buffer layer is a solar cell formed to a thickness of 50nm to 80nm. Forming a back electrode layer on the support substrate;
Forming a light absorbing layer on the back electrode layer;
Forming a buffer layer doped with Cu on the light absorbing layer; And
Forming a window layer on the buffer layer; The method according to claim 6,
The buffer layer is a solar cell manufacturing method is formed by the method of Chemical Bath Deposition (CBD) by mixing Thiourea (Thiourea), NH ₄ OH, Cd-salt, Cu-salt. The method of claim 7, wherein
The CBD is a solar cell manufacturing method that proceeds for a time of 10 minutes to 15 minutes at a temperature of 60 ℃ to 80 ℃. The method of claim 7, wherein
The Cd-salt is CdSO ₄ , Cd (ac) ₂ , CdCl ₂ At least one of, Cu-salt is CuSO ₄ , Cu (ac) ₂ , CuCl ₂ Solar cell manufacturing method comprising at least one of.

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