KR101189432B1 - Solar cell apparatus and method of fabricating the same - Google Patents

Abstract

Solar cell according to the embodiment is a substrate; A back electrode layer on the substrate; A light absorbing layer on the back electrode layer; A buffer layer on top of the light absorbing layer; And a window layer on the buffer layer, wherein the back electrode layer includes first through grooves and side surfaces of the first through grooves are inclined with an upper surface of the substrate.

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

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

In addition, various studies are underway to increase the efficiency of such solar cells.

The embodiment provides a solar cell having improved reliability and a method of manufacturing the same.

Solar cell according to the embodiment is a substrate; A back electrode layer on the substrate; A light absorbing layer on the back electrode layer; A buffer layer on top of the light absorbing layer; And a window layer on the buffer layer, wherein the back electrode layer includes first through grooves and side surfaces of the first through grooves are inclined with an upper surface of the substrate.

A method of manufacturing a solar cell according to an embodiment includes forming a back electrode layer on a substrate; Etching a portion of the back electrode layer to expose the top surface of the substrate; And forming a light absorbing layer, a buffer layer, and a window layer on the back electrode layer, and etching the part of the back electrode layer is irradiated in a direction in which a laser is inclined with respect to an upper surface of the substrate.

According to the embodiment, the side surface of the back electrode layer which is separated into a plurality by the first through grooves is formed to be inclined with the substrate. Accordingly, when the first through holes are formed, burrs may be prevented from occurring due to thermal shock caused by a laser.

In addition, since the coverage defects can be prevented from being caused by the first through holes formed to have the substrate and the inclined surface, it is possible to provide a solar cell having improved reliability.

1 is a plan view illustrating a solar cell apparatus according to an embodiment.
FIG. 2 is a cross-sectional view illustrating a cross section taken along AA ′ in FIG. 1.
3 is an enlarged cross-sectional view of B of FIG. 2.
4 to 7 are cross-sectional views illustrating a method of manufacturing a solar cell according to an embodiment.

In the description of the embodiments, when each support substrate, layer, film, or electrode is described as being formed "on" or "under" of each support substrate, layer, film, or electrode, etc. As used herein, “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.

FIG. 1 is a plan view illustrating a photovoltaic device according to an embodiment, and FIG. 2 is a cross-sectional view illustrating a cross section taken along a line A-A 'of FIG. 1.

2, a solar cell according to an embodiment includes a support substrate 100, a back electrode layer 200 on the support substrate 100, a light absorbing layer 300 on the back electrode layer 200, and the light absorbing layer. A buffer layer 400 and a high resistance buffer layer 500 on the 300 and a window layer 600 on the high resistance buffer layer 500 are included.

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

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

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.

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, since the back electrode layer 200 is in contact with the CIGS compound forming the light absorbing layer 300, the light absorbing layer 300 and the back electrode layer 200 should be an ohmic contact having a small contact resistance value.

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). Among them, in particular, molybdenum (Mo) has a small difference between the support substrate 100 and the coefficient of thermal expansion compared to other elements, and thus excellent adhesion can be prevented from occurring in the peeling phenomenon. Overall required properties can be met.

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.

First through holes TH1 are formed in the back electrode layer 200. The first through holes TH1 are open regions exposing a portion of an upper surface of the support substrate 100. The first through holes TH1 may have a shape extending in one direction when viewed in a plan view.

The width of the support substrate 100 exposed by the first through holes TH1 may be about 20 μm to 150 μm.

The back electrode layer 200 is divided into a plurality of back electrodes by the first through holes TH1. That is, back electrodes are defined by the first through holes TH1.

The back electrodes are arranged in a stripe shape. Alternatively, the back electrodes may be arranged in a matrix form. At this time, the first through grooves TH1 may be formed in a lattice form when viewed from a plane.

The first through holes TH1 are patterned by a laser. In the case of conventional laser patterning incident in a direction perpendicular to the substrate to form the first through holes TH1, a burr is formed on the back electrode layer 200 by air expansion and thermal shock at the laser irradiation site. May occur.

When the burr is patterned on the back electrode layer 200, the burr refers to a thinly curled processing mark that occurs at an edge portion of the first through holes TH1.

In the case of a large-area solar cell, the back electrode layer grown on the support substrate may be formed of a plurality of layers having different densities, in which case the lower back electrode layer in contact with the support substrate may be used to improve adhesion to the support substrate. It can be formed at a low density, and the upper back electrode layer in contact with the light absorbing layer can be formed at a relatively high density in consideration of electrical conductivity.

As described above, when a plurality of layers having different densities are grown, the thermal expansion coefficient of the lower back electrode layer having a relatively low density due to thermal shock caused by a laser during the patterning process for forming the first through holes TH1 is relatively. It can have a large value. As a result, since the lower back electrode layer is more expanded than the upper back electrode layer, the edge of the back electrode layer on which the first through holes TH1 are formed may be curved toward the top.

In addition, in the case where the first through holes TH1 are formed in the back electrode layer by injecting the laser vertically, the light absorbing layer grown after the growth is not formed uniformly but is formed in a shape where grains are combined to cover coverage. Defects may occur.

As a result, current loss occurs at the grain interface. In addition, since the grains may be formed spaced apart from the substrate, the reliability of the device may be improved.

3 is an enlarged cross-sectional view of B of FIG. 2. According to the exemplary embodiment of the present invention, the side surfaces 210 and 220 of the first through holes TH1 may be formed to have an inclination angle θ with a vertical line of the substrate. The θ may be formed in the range of 10 ° <θ ≦ 80 °. Preferably, when θ exceeds 80 °, the distance between adjacent back electrodes increases, so that the photovoltaic region is relatively reduced, and if the angle is less than 30 °, the distance between adjacent back electrodes becomes narrower. Short may occur between the battery cells, and preferably, θ may be formed in a range of 30 ° ≦ θ ≦ 60 °.

Side surfaces 210 and 220 of the first through holes TH1 may be formed at the same angle or have different values within the range.

According to the angle θ, the back electrode layer 200 may be formed in a trapezoidal shape having different upper and lower etching areas. That is, in order to form the first through holes TH1, the laser may be incident to the vertical plane of the substrate in a plurality of directions so as to be inclined so that the etching area thereof becomes wider.

As described above, since the plurality of lasers are inclined to each other and the first through holes TH1 are formed, the side surface of the back electrode layer 200 is formed to have the inclined surface of the support substrate 100. That is, the etching area increases from the support substrate 100 toward the upper portion thereof, and thus, the width of the first through holes TH1 may increase from the supporting substrate 100 upward. Accordingly, the probability of occurrence of burrs due to the difference in thermal expansion coefficients of the upper and lower backside electrode layers is reduced, so that the reliability of the device can be improved.

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 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 And a copper-zinc-tin-selenide-based crystal structure.

The buffer layer 400 and the high resistance buffer layer 500 may be formed 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 thin film as the n-type semiconductor. However, since the two materials have a large difference in lattice constant and band gap energy, a buffer layer having a band gap in between the two materials is required to form a good junction.

Materials for forming the buffer layer 400 include II-VI groups such as CdS and ZnS, and CdS is relatively excellent in terms of power generation efficiency of solar cells.

The high resistance buffer layer 500 includes zinc oxide (i-ZnO) that is not doped with impurities. The energy bandgap of the high resistance buffer layer 500 is about 3.1 eV to 3.3 eV.

The window layer 600 is formed 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 oxide may include conductive impurities such as aluminum (Al), alumina (Al ₂ O ₃ ), magnesium (Mg), or gallium (Ga). In more detail, the window layer 600 may include aluminum doped zinc oxide (AZO), gallium doped zinc oxide (GZO), or the like.

As discussed above, since the first through holes TH1 are formed to have a surface inclined with the vertical line of the support substrate 100, the burrs may be formed by thermal shock caused by a laser when the first through holes TH1 are formed. It is possible to prevent the occurrence of burrs.

In addition, since the coverage failure may be prevented by the first through holes TH1 formed to have the substrate and the inclined surface, the solar cell having improved reliability may be provided.

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

Referring to FIG. 4, the back electrode layer 200 is formed on the support substrate 100, and the back electrode layer 200 is patterned to form first through holes TH1. Accordingly, a plurality of back electrodes are formed on the support substrate 100. The back electrode layer 200 is patterned by a laser.

The first through holes TH1 expose the upper surface of the supporting substrate 100 and may have a width of about 80 mu m to about 200 mu m.

In addition, an additional layer, such as a diffusion barrier, may be interposed between the support substrate 100 and the back electrode layer 200, wherein the first through holes TH1 expose the top surface of the additional layer. .

The first through holes TH1 may be formed to have an inclined side surface. To this end, a plurality of lasers may be formed to have an inclination angle θ with respect to the vertical line of the support substrate 100. According to the angle θ, the back electrode layer 200 may be formed in a trapezoidal shape having different upper and lower etching areas. That is, in order to form the first through holes TH1, the laser may be incident to the vertical plane of the substrate in a plurality of directions so as to be inclined so that the etching area thereof becomes wider.

The focus of the plurality of lasers is preferably formed so as not to overlap with each other by more than 40%.

The first through holes TH1 may be formed by, for example, a laser having a wavelength of about 500 to 1200 nm.

Referring to FIG. 5, the light absorbing layer 300, the buffer layer 400, and the high resistance buffer layer 500 are formed on the back electrode layer 200.

The light absorption layer 300 may be formed by a sputtering process or an evaporation process.

For example, a copper-indium-gallium-selenide (Cu (In, Ga) Se ₂ ; CIGS system) is formed while simultaneously evaporating copper, indium, gallium, and selenium to form the light absorption layer 300. A method of forming a light absorbing layer 300 of a metal precursor film and a method of forming a metal precursor film by a selenization process are widely used.

When the metal precursor film is formed and selenization is subdivided, a metal precursor film is formed on the back electrode 200 by a sputtering process using a copper target, an indium target, and a gallium target.

Then, the metal precursor film is formed with a light absorbing layer 300 of copper-indium-gallium-selenide (Cu (In, Ga) Se _2, CIGS system) 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.

Thereafter, cadmium sulfide is deposited by a sputtering process or a chemical bath depositon (CBD) or the like, and the buffer layer 400 is formed.

Thereafter, a portion of the light absorbing layer 300, the buffer layer 400, and the high resistance buffer layer 500 is removed to form second through holes TH2.

The second through holes TH2 may be formed by a mechanical device such as a tip or a laser device.

For example, the light absorbing layer 300 and the buffer layer 400 may be patterned by a tip having a width of about 40 μm to about 180 μm. In addition, the second through holes TH2 may be formed by a laser having a wavelength of about 200 to 600 nm.

In this case, the width of the second through holes TH2 may be about 30 μm to about 100 μm. In addition, the second through holes TH2 are formed to expose a portion of the top surface of the back electrode layer 200.

Referring to FIG. 6, a window layer 600 is formed on the light absorbing layer 300 and inside the second through holes TH2. That is, the window layer 600 is formed by depositing a transparent conductive material on the buffer layer 400 and inside the second through holes TH2.

In this case, the transparent conductive material is filled in the second through holes TH2, and the window layer 600 is in direct contact with the back electrode layer 200.

In this case, the window layer 600 may be formed by depositing the transparent conductive material in an oxygen-free atmosphere. In more detail, the window layer 600 may be formed by depositing zinc oxide doped with aluminum in an inert gas atmosphere containing no oxygen.

Next, a portion of the buffer layer 400, the high resistance buffer layer 500, and the window layer 600 is removed to form third through holes TH3. Accordingly, the window layer 600 is patterned to define a plurality of windows and a plurality of cells C1, C2... The width of the third through holes TH3 may be about 30 μm to about 200 μm.

The connection parts 700 are disposed inside the second through holes TH2. The connection parts 700 extend downward from the window layer 600 and are connected to the back electrode layer 200. For example, the connection parts 700 extend from the window of the first cell and are connected to the back electrode of the second cell.

Thus, the connection parts 700 connect adjacent cells to each other. In more detail, the connection parts 700 connect the windows and the back electrodes included in the cells C1 and C2... Adjacent to each other.

The connection part 700 is formed integrally with the window layer 600. That is, the material used as the connection part 700 is the same as the material used as the window layer 600.

Referring to FIG. 7, portions of the buffer layer 400, the high resistance buffer layer 500, and the window layer 600 are removed to form third through holes TH3. Accordingly, the window layer 600 is patterned to define a plurality of windows and a plurality of cells C1, C2... As described above, according to the embodiment, it is possible to prevent a phenomenon in which burrs are generated by thermal shock caused by a laser when forming the first through holes, and provide a solar cell having improved reliability.

In addition, 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 (10)

Board;
A back electrode layer on the substrate;
A light absorbing layer on the back electrode layer;
A buffer layer on top of the light absorbing layer; And
And a window layer on the buffer layer.
The back electrode layer includes first through grooves and side surfaces of the first through grooves are formed to be inclined with an upper surface of the substrate.
The back electrode layer is formed of a plurality of layers,
The plurality of back electrode layers are formed such that the upper back electrode layer has a higher particle density than the lower back electrode layer. The method of claim 1,
The side surface of the back electrode layer having the first through grooves is formed to have a slope of 30 ° to 60 ° with a vertical line of the substrate. delete delete The method of claim 1,
The first through holes are formed in a width of 20㎛ to 150㎛ solar cell. delete Forming a back electrode layer on the substrate;
Etching a portion of the back electrode layer to expose the top surface of the substrate; And,
Forming a light absorbing layer, a buffer layer, and a window layer on the back electrode layer;
Etching a portion of the back electrode layer, the laser is irradiated in a direction inclined with respect to the upper surface of the substrate,
Forming the back electrode layer,
Forming a lower back electrode layer adjacent the substrate; And,
And forming an upper back electrode layer formed on the lower back electrode layer and having a relatively higher particle density than the lower back electrode layer. The method of claim 7, wherein
The laser is irradiated a plurality of times, symmetrical with respect to the vertical line of the substrate, the incident method of the solar cell is incident to have a slope of 30 ° to 60 ° with respect to the vertical line of the substrate, respectively. The method of claim 7, wherein
The first through holes are formed by injecting a laser having a wavelength of 500nm to 1200nm. delete

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