KR101326968B1 - 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 on the support substrate; And a light absorption layer on the back electrode layer, wherein the light absorption layer has a plurality of layers stacked thereon, and a band gap is improved toward an upper portion thereof.

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.

Recently, as energy resources such as petroleum and coal are expected to be depleted, interest in alternative energy to replace them is increasing, and solar cells that produce electric energy from solar energy are attracting attention.

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 are formed in 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.

Charge and holes are generated by sunlight, and when the same amount of light is received, the efficiency of the solar cell is determined by how many electrons and holes can be accumulated. That is, the efficiency is determined by reducing defects that serve as recombination sites of electron-holes generated in the light absorbing layer.

However, when a large amount of catalyst metal is present in the photo-defective layer, electron-hole pairs generated by sunlight are separated by an electric field, and recombination occurs due to electrons and holes existing in impurities, thereby preventing accumulation.

In conclusion, the more impurities in the light absorbing layer, the higher the recombination frequency, and thus, there is a problem in that the charge accumulation probability, that is, efficiency of the solar cell decreases.

In general, a solar cell has a grain boundary as an electron-hole recombination defect, that is, a recombination site. do.

Solar cell according to an embodiment of the present invention; A back electrode layer on the support substrate; And a light absorption layer on the back electrode layer, wherein the light absorption layer has a plurality of layers stacked thereon, and a band gap is improved toward an upper portion thereof.

In the solar cell according to the embodiment of the present invention, the magnetic layer is deposited on the back electrode layer, thereby improving the generation of electron-holes and suppressing recombination, thereby improving photoelectric conversion efficiency.

1 is a cross-sectional view showing a solar cell according to an embodiment.
2 is a graph showing a band gap according to a ratio of materials included in a light absorbing layer.
3 is a photograph showing grain according to the ratio of Ga.
4 to 6 are cross-sectional views showing a method of manufacturing a solar cell according to the embodiment.

In the description of the embodiments, in the case where each substrate, layer, film or electrode is described as being formed "on" or "under" of each substrate, layer, film, , "On" and "under" all include being formed "directly" or "indirectly" through "another element". 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. 2 is a graph showing a band gap according to a ratio of materials included in a light absorbing layer. 3 is a photograph showing grain according to the ratio of Ga.

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, and a window layer 500.

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

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 can be a factor for increasing the photoelectric conversion efficiency of the solar cell.

The back electrode layer 200 is disposed on the support substrate 100. The rear electrode layer 200 is a conductive layer. The back electrode layer 200 may allow electric charges generated in the light absorbing layer 300 of the solar cell to move to allow current to flow 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 should maintain high temperature stability during heat treatment under sulfur (S) or selenium (Se) atmosphere accompanying CIGS compound formation. In addition, the back electrode layer 200 should be excellent in adhesion with the support substrate 100 so that peeling does not occur with the support substrate 100 due to a difference in thermal expansion coefficient.

As the material for forming the back electrode layer 200, a material having a low difference between the support substrate 100 and the coefficient of thermal expansion should be considered to have excellent adhesiveness and to prevent peeling from occurring. Molybdenum (Mo) may be used as such a material.

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 light absorbing layer 300 includes a first light absorbing layer 310, a second light absorbing layer 320 formed on the first light absorbing layer 310, and a third light formed on the second light absorbing layer 320. An absorber layer 330 is included.

In the exemplary embodiment, three light absorbing layers are illustrated, but the present invention is not limited thereto and may be formed by stacking two or four or more layers.

For example, when the light absorbing layer is stacked in four layers, the first light absorbing layer 310 is InGaSe, the second light absorbing layer 320 is CuSe, and the third light absorbing layer 330 is InSe, the first light absorbing layer May be formed to include Al.

Adjacent light absorbing layers in the first light absorbing layer 310, the second light absorbing layer 320, and the third light absorbing layer 330 may be formed of different materials.

The energy band gap of the first light absorbing layer 310, the second light absorbing layer 320, and the third light absorbing layer 330 may be sequentially improved. That is, the first light absorbing layer 310 has a low energy band gap and may be formed to have a relatively highest energy band gap in the third light absorbing layer 330.

As shown in FIG. 2, the energy band gap varies depending on the material included.

The first light absorbing layer 310 may be formed to have a bandgap of 1.1 eV to 1.5 eV, the second light absorbing layer 320 to 1.1 eV to 1.7 eV, and the third light absorbing layer 330 to 1.1 eV to 2.7 eV. It is formed to increase the band gap toward the top.

The first light absorbing layer 310 may be formed of CuIn (Se _(1-x) S _x ) ₂ , and the second light absorbing layer 320 is formed of Cu (In _(1-x) Ga _x ) Se ₂ . The third light absorbing layer 330 may be formed of a chemical formula of Cu (In _(1-x) Al _x ) Se ₂ (0 <x ≦ 1).

In addition, the first light absorbing layer 310 may be formed of InGaSe, the second light absorbing layer 320 may be formed of the chemical formula of CuSe, and the third light absorbing layer 330 may be formed of InAlSe.

In a typical solar cell, the light absorbing layer 300 is formed of a P layer and the window layer 500 is formed of an N layer. When the light absorbing layer is formed of one layer, the band gap is fixed, so that the band energy band gap is fixed. It is limited in the implementation of a solar cell having a.

In the present invention, the band gap increases among the first light absorbing layer 310, the second light absorbing layer 320, and the third light absorbing layer 330 having different band gaps as described above. By depositing the material it is possible to improve the photo-electric conversion efficiency through Voc enhancement.

3 is a photograph showing grain according to the ratio of Ga. Ga is used in the light absorbing layer 300 that operates as a P-type semiconductor layer. The Ga is expensive, and as shown in FIG. 3, when the content of Ga increases in the light absorbing layer, grain boundary increases. The defect will increase. As a result, recombination of electrons and holes occurs in the defect region, thereby reducing photoelectric conversion efficiency.

That is, in general Ga back gradation, since grain growth is suppressed in the space charge region by addition of Ga due to gradation, and a defect is increased, a certain amount of Ga cannot be added, but the magnetic layer according to the embodiment of the present invention. By 300, the same effect as backgrading can be obtained without adding Ga, so that the photo-electric conversion efficiency can be improved.

In the embodiment of the present invention, since the light conversion layer having the bandgap that sequentially increases from the rear electrode layer toward the buffer layer is formed as described above, short-circuit current density (Jsc) may increase.

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 500 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 relatively excellent in terms of power generation efficiency of the solar cell. When the buffer layer 400 does not include cadmium (Cd) such as ZnS, the bandgap arrangement of the light absorbing layer 300 is easy.

The buffer layer 400 may be formed to a thickness of 10nm to 100nm, preferably 50nm to 80nm.

A high resistance buffer layer (not shown) 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.

The window layer 500 is disposed on the buffer layer 400. The window layer 500 is transparent and a conductive layer. In addition, the resistance of the window layer 500 is higher than that of the back electrode layer 200.

The window layer 500 includes an oxide. For example, the window layer 500 may include zinc oxide, indium tin oxide (ITO), or indium zinc oxide (IZO).

In addition, the window layer 500 may include aluminum doped zinc oxide (AZO) or gallium doped zinc oxide (GZO).

The solar cell according to the embodiment may deposit a magnetic layer on the rear electrode layer to improve the generation of electron-holes and to suppress recombination, thereby improving photoelectric conversion efficiency.

4 to 6 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. 4, the back electrode layer 200 is formed on the support substrate 100. The back electrode layer 200 may be deposited using molybdenum.

Referring to FIG. 5, a light absorbing layer 300 may be formed on the back electrode layer 200. The light absorbing layer 300 may be, for example, copper, indium, gallium, or selenium while simultaneously or separately evaporating a copper-indium-gallium-selenide-based (Cu (In, Ga) Se 2; CIGS-based) light absorbing layer ( A method of forming 300 and a method of forming a metal precursor film and then forming it by a selenization process are widely used.

When a metal precursor film is formed and then subjected to selenization, a metal precursor film is formed on the rear electrode 200 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 300 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.

The light absorbing layer 300 may be formed by sequentially including the first, second, and third light absorbing layers 310, 320, and 330. The material of each layer is different, and the light absorbing layer 300 may be formed by a chemical formula in which a band gap increases toward an upper portion.

Referring to FIG. 6, a buffer layer 400 is formed on the light absorbing layer 300. The buffer layer 400 may include CdS or ZnS, and may be formed by PVD or plating.

Thereafter, the window layer 500 is formed on the buffer layer 400. The window layer 500 is formed by depositing a transparent conductive material on the buffer layer 400.

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 (11)

A support substrate;
A back electrode layer on the support substrate; And
And a light absorption layer on the rear electrode layer.
The light absorbing layer is a plurality of layers are stacked, the band gap becomes higher toward the top,
The light absorbing layer,
A first light absorbing layer, a second light absorbing layer, and a third light absorbing layer sequentially stacked on the back electrode layer;
The first light absorbing layer is formed of CuIn (Se _(1-x) S _x ) ₂ , the second light absorbing layer is formed of Cu (In _(1-x) Ga _x ) Se ₂ , and the third light absorbing layer is Cu (In _(1-x) Al _x ) Se ₂ A solar cell formed by the chemical formula (0 <x≤1). The method of claim 1,
The first light absorbing layer to the third light absorbing layer has a bandgap of 1.1eV to 2.7eV,
A solar cell of which a band gap increases from the first light absorbing layer to the third light absorbing layer. delete delete The method of claim 1,
A first light absorbing layer, a second light absorbing layer, and a third light absorbing layer sequentially stacked on the back electrode layer;
The first light absorbing layer is formed of InGaSe, the second light absorbing layer is formed of CuSe, and the third light absorbing layer is formed of the chemical formula of InAlSe. delete The method of claim 1,
And a buffer layer formed on the light absorbing layer, wherein the buffer layer is formed of ZnS. Forming a back electrode layer on the support substrate;
Forming a first light absorbing layer on the back electrode layer; And
And forming a second light absorbing layer on the first light absorbing layer, the second light absorbing layer having a higher bandgap than the first light absorbing layer.
The first light absorbing layer is formed of CuIn (Se _(1-x) S _x ) ₂ , and the second light absorbing layer is represented by the chemical formula of Cu (In _(1-x) Ga _x ) Se ₂ (0 <x≤1). Formed solar cell manufacturing method. delete 9. The method of claim 8,
A third light absorbing layer is formed on the second light absorbing layer, and the third light absorbing layer is formed using a chemical formula of Cu (In _(1-x) Al _x ) Se ₂ (0 <x≤1). . 9. The method of claim 8,
The first light absorbing layer is formed on the back electrode layer by the formula of InGaSe, the second light absorbing layer is formed by the formula of CuSe, and the third light absorbing layer is formed of the formula of InAlSe.

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