JP2014503130A - Solar cell and manufacturing method thereof - Google Patents

Abstract

A solar cell according to the present invention includes a substrate, a back electrode layer on the substrate, a light absorption layer on the back electrode layer, a buffer layer on the light absorption layer, and on the buffer layer. The back electrode layer includes a first through groove, and a side surface of the first through groove is formed to be inclined with respect to the upper surface of the substrate.
[Selection] Figure 2

Description

  The disclosed embodiments relate to a solar cell and a method for manufacturing the solar cell.

  Recently, as the demand for energy increases, the development of solar cells that convert solar energy into electrical energy has been promoted.

  In particular, CIGS solar cells, which are pn heterojunction devices having a support substrate structure including a glass support substrate, a metal back electrode layer, a p-type CIGS light absorbing portion, a buffer layer, an n-type transparent electrode layer, etc., are widely used. .

  In addition, various studies are being carried out to increase the efficiency of such solar cells.

  An embodiment of the disclosure is to provide a solar cell with improved reliability and a method for manufacturing the same.

  A solar cell according to an embodiment of the present invention includes a substrate, a back electrode layer on the substrate, a light absorption layer on the back electrode layer, a buffer layer on the light absorption layer, and a window layer on the buffer layer. The back electrode layer includes a first through groove, and a side surface of the first through groove is formed to be inclined with respect to the upper surface of the substrate.

  A method of manufacturing a solar cell according to an embodiment of the present invention includes a step of forming a back electrode layer on a substrate, a step of etching a part of the back electrode layer so as to expose an upper surface of the substrate, and the back electrode Forming a light absorption layer, a buffer layer, and a window layer on the layer, and etching the part of the back electrode layer in a direction in which the laser is inclined with respect to the upper surface of the substrate Is irradiated.

  According to the present invention, the side surface of the back electrode layer separated into a plurality by the first through groove is formed to have an inclination with respect to the substrate. As a result, when the first through groove is formed, it is possible to prevent a phenomenon in which a burr is caused by a thermal shock caused by a laser.

  In addition, since the first through groove formed to have a substrate and an inclined surface can prevent a coverage defect from occurring, a solar cell with improved reliability can be provided.

It is a top view which shows the solar power generation device by embodiment of this invention. It is sectional drawing which shows the cross section cut | disconnected along А-А 'in FIG. It is sectional drawing to which B of FIG. 2 was expanded. It is sectional drawing which shows the manufacturing method of the solar cell by embodiment of this invention. It is sectional drawing which shows the manufacturing method of the solar cell by embodiment of this invention. It is sectional drawing which shows the manufacturing method of the solar cell by embodiment of this invention. It is sectional drawing which shows the manufacturing method of the solar cell by embodiment of this invention.

  In describing the present invention, each support substrate, layer, membrane, or electrode is formed “on” or “under” each support substrate, layer, membrane, electrode, or the like. Where “on” and “under” include all being “directly” or “indirectly” formed.

  Further, the reference to the top or bottom of each component will be described with reference to the drawings.

  In the drawings, the size of each component may be exaggerated for the purpose of explanation, and does not mean a size that is actually applied.

  FIG. 1 is a plan view showing a photovoltaic power generation apparatus according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a cross section taken along the line А-А 'in FIG.

  Referring to FIG. 2, a solar cell according to an embodiment of the present invention includes a support substrate 100, a back electrode layer 200 on the support substrate 100, a light absorption layer 300 on the back electrode layer 200, and the light absorption layer. 300 includes a buffer layer 400 on 300, a high-resistance buffer layer 500, and a window layer 600 on the high-resistance buffer layer 500.

  The support substrate 100 has a plate shape, and supports the back electrode layer 200, the light absorption layer 300, the buffer layer 400, the high resistance buffer layer 500, and the window layer 600. The support substrate 100 is an insulator, the support substrate 100 is a glass substrate, a plastic substrate, or a metal substrate. More specifically, the support substrate 100 is a soda lime glass. It can be a substrate.

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

  In addition, as the material of the support substrate 100, a ceramic substrate such as alumina, stainless steel, a flexible polymer, or the like is used. The support substrate 100 is 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 an electric current to flow outside the solar cell such that the charge generated in the light absorption layer 300 of the solar cell moves.

  The back electrode layer 200 must have high electrical conductivity and low specific resistance in order to perform such a function.

  In addition, since the back electrode layer 200 is in contact with the CIGS compound forming the light absorption layer 300, the light absorption layer 300 and the back electrode layer 200 must be a resistive contact having a small contact resistance value. I must.

  Further, the back electrode layer 200 must maintain high-temperature safety during heat treatment in an atmosphere of sulfur (S) or selenium (Se) associated with formation of a CIGS compound. In addition, the back electrode layer 200 must have excellent adhesion to the support substrate 100 so that a peeling phenomenon does not occur from the support substrate 100 due to a difference in thermal expansion coefficient.

  Such a back electrode layer 200 is formed of any one of molybdenum (Mo), gold (Au), aluminum (Al), chromium (Cr), tungsten (W), and copper (Cu). Among these, in particular, molybdenum (Mo) is excellent in adhesion because the difference between the thermal expansion coefficient and the support substrate 100 is small compared to other elements, and can prevent the peeling phenomenon from occurring. The characteristics required for the back electrode layer 200 described above can be generally satisfied.

  The back electrode layer 200 may include two or more layers. At this time, each layer is formed of the same metal or different metals.

  The back electrode layer 200 is formed with a first through groove (TH1). The first through groove (TH1) is an open region that exposes a part of the upper surface of the support substrate 100. The first through groove (TH1) has a shape extending in one direction in a plan view.

The width of the support substrate 100 exposed by the first through groove TH1 is about 20 μm to 150 μm.
The back electrode layer 200 is divided into a large number of back electrodes by the first through grooves TH1. That is, the back electrode is defined by the first through groove (TH1).

  The back electrodes are arranged in a stripe shape. In contrast, the back electrodes may be arranged in a matrix. At this time, the first through groove TH1 may be formed in a lattice shape in plan view.

The first through groove (TH1) is patterned by a laser. In the case of the existing laser patterning incident on the substrate in a direction perpendicular to the substrate in order to form the first through groove TH1, the back electrode layer 200 is formed by air expansion at the laser irradiation site and thermal shock. Burr may occur in the surface.
The burr means a processing trace having a thin end wound around the edge of the first through groove (TH1) when patterning is performed on the back electrode layer 200.

  In the case of a large-area solar cell, the back electrode layer grown on the support substrate may be formed into a plurality of layers with different densities. In this case, the lower back electrode layer in contact with the support substrate In order to improve adhesion to the substrate, it can be formed at a low density, and the upper back electrode layer in contact with the light absorption 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, during the patterning process for forming the first through-groove (TH1), the lower density of the lower portion is caused by the thermal shock caused by the laser. The thermal expansion coefficient of the back electrode layer may have a relatively large value.

  As a result, the lower back electrode layer expands further relative to the upper back electrode layer, so that the vicinity of the edge of the back electrode layer in which the first through groove (TH1) is formed bends upward. It may be formed in a rare shape.

  Further, when the first through-groove (TH1) is formed in the back electrode layer by vertically entering the laser, the light absorption layer grown thereafter is not uniformly grown, and the shape is adjusted to the grain. In some cases, a coverage failure may occur.

  As a result, a current loss occurs at the grain interface. Further, since the grain may be formed apart from the substrate, there is room for improvement in the reliability of the element.

  FIG. 3 is an enlarged cross-sectional view of B of FIG. According to an embodiment of the present invention, the side surfaces 210 and 220 of the first through groove TH1 may be formed to have an angle (θ) inclined with respect to the vertical line of the substrate.

  When the angle θ exceeds 80 °, the distance between the adjacent backside electrodes increases, so the photovoltaic region decreases relatively. When the angle is less than 30 °, the distance between the adjacent backside electrodes becomes narrower. Thus, a short circuit may occur between adjacent solar cells, so that the θ is formed in the range of 10 ° <θ ≦ 80 °, or preferably 30 ° ≦ θ ≦ 60. It is formed in the range of °.

  The side surfaces 210 and 220 of the first through groove (TH1) are formed at the same angle or have different values within the range.

  Depending on the angle (θ), the back electrode layer 200 may be formed in a trapezoidal shape with different etching areas at the top and bottom. That is, in order to form the first through-groove (TH1), the laser beam is incident on the vertical surface of the substrate in a plurality of directions so as to be inclined, and the etching area is increased toward the top. The

  As described above, since the plurality of lasers are incident on each other at an angle to form the first through groove (TH1), the side surface of the back electrode layer 200 is formed to have a slope with the support substrate 100. The

  That is, the etching area increases from the support substrate 100 to the top, and the width of the first through groove (TH1) increases from the top. As a result, the probability of occurrence of burrs due to the difference in thermal expansion coefficient between the upper and lower back electrode layers is reduced, so that the reliability of the element is improved.

A light absorption layer 300 is formed on the back electrode layer 200. The light absorption layer 300 includes a p-type semiconductor compound. More specifically, the light absorption layer 300 includes a group I-III-VI related compound. For example, the light absorption layer 300 includes a copper-indium-gallium-selenide-based (Cu (In, Ga) Se ₂ ; CIGS-based) crystal structure, a copper-indium-selenide-based, or a copper-gallium-selenide-based, copper- It has a zinc-tin-selenide crystal structure.

  A buffer layer 400 and a high resistance buffer layer 500 are formed on the light absorption layer 300. In a solar cell having a CIGS compound as the light absorption layer 300, a pn junction is formed between a CIGS compound thin film that is a p-type semiconductor and a window layer 600 thin film that is an 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 the band gap is located between the two materials is necessary to form a good junction.

  Examples of the material 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 the solar cell.

  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 is about 3.1 eV to 3.3 eV.

  A window layer 600 is formed on the high resistance buffer layer 500. The window layer 600 is transparent and is a conductive layer. Further, 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 includes zinc oxide, indium tin oxide (ITO), indium zinc oxide (IZO), or the like.

The oxide includes a conductive impurity such as aluminum (Al), alumina (Al ₂ O ₃ ), magnesium (Mg), or gallium (Ga). More specifically, the window layer 600 includes aluminum doped zinc oxide (AZO) or gallium doped zinc oxide (GZO).

  As discussed above, the first through groove (TH1) is formed so as to have a surface inclined with respect to the vertical line of the support substrate 100. Therefore, when forming the first through groove (TH1), a laser is used. It is possible to prevent the occurrence of burr due to thermal shock.

  In addition, since the first through groove (TH1) formed so as to have the substrate and the slope can prevent the occurrence of a coverage defect, a solar cell with improved reliability can be provided.

  4 to 7 are cross-sectional views illustrating a method for manufacturing a photovoltaic power generator according to an embodiment of the present invention. The description regarding the manufacturing method of the present invention refers to the above-described description regarding the photovoltaic power generation apparatus.

  Referring to FIG. 4, a back electrode layer 200 is formed on the support substrate 100, and the back electrode layer 200 is patterned to form a first through groove (TH1). As a result, a number of back electrodes are formed on the support substrate 100. The back electrode layer 200 is patterned by a laser.

  The first through groove TH1 exposes the upper surface of the support substrate 100 and has a width of about 80 μm to 200 μm.

  In addition, an additional layer such as a diffusion barrier layer may be interposed between the support substrate 100 and the back electrode layer 200. At this time, the first through groove (TH1) The upper surface of the additional layer is exposed.

  The first through groove TH1 may be formed such that a side surface has an inclination. Therefore, the plurality of lasers are formed to have an angle (θ) inclined with respect to the vertical line of the support substrate 100.

  Depending on the angle (θ), the back electrode layer 200 is formed in a trapezoidal shape with different etching areas at the top and bottom. That is, in order to form the first through-groove (TH1), a laser is incident on the vertical surface of the substrate in a plurality of directions with an inclination, and the etching area is increased as it goes upward. be able to.

  It is preferable that the first through grooves are formed so that the focus of the plurality of lasers overlap each other by 5% or more and 60% or less.

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

  Referring to FIG. 5, a light absorption layer 300, a buffer layer 400, and a 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 method. For example, in order to form the light absorption layer 300, copper, indium, gallium, and selenium are vaporized simultaneously or separately, and copper-indium-gallium-selenide system (Cu (In, Ga) Se ₂ ; CIGS system). ) And a method of forming a metal precursor film and then forming it by a selenization process are widely used.

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

Thereafter, a light absorption layer 300 of a copper-indium-gallium-selenide system (Cu (In, Ga) Se ₂ ; CIGS system) is formed on the metal precursor film by a selenization process.

  In contrast, the sputtering process using the copper target, the indium target, and the gallium target, and the selenization process may be performed simultaneously.

  Further, the CIS-based or CIG-based light absorption layer 300 is 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 sputtering or chemical bath deposition (CBD) to form the buffer layer 400.

  Thereafter, the light absorption layer 300, the buffer layer 400, and the high resistance buffer layer 500 are partially removed to form a second through groove (TH2).

  The second through groove (TH2) may be formed by a mechanical device such as a chip or a laser device.

  For example, the light absorption layer 300 and the buffer layer 400 are patterned using a chip having a width of about 40 μm to 180 μm. Further, the second through groove (TH2) is formed by a laser having a wavelength of about 200 to 600 nm.

  At this time, the width of the second through groove TH2 may be about 30 um to 100 um.

  Further, the second through groove (TH2) is formed so as to expose a part of the upper surface of the back electrode layer 200.

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

  At this time, the transparent conductive material is filled inside the second through-groove (TH2), and the window layer 600 comes into direct contact with the back electrode layer 200.

  Here, the window layer 600 may be formed by depositing the transparent conductive material in an oxygen-free atmosphere. More specifically, the window layer 600 may be formed by depositing zinc oxide doped with aluminum in an inert gas atmosphere not containing oxygen.

  Next, the buffer layer 400, the high-resistance buffer layer 500, and the window layer 600 are partially removed to form a third through groove TH3. Accordingly, the window layer 600 is patterned to define a large number of windows and a large number of cells (C1, C2,...). The width of the third through groove (TH3) is about 30 μm to 200 μm.

  The connecting portion 700 is disposed inside the second through groove (TH2). The connection part 700 extends downward from the window layer 600 and is connected to the back electrode layer 200. For example, the connection part 700 extends from the window of the first cell and is connected to the back electrode of the second cell.

  Accordingly, the connection unit 700 connects adjacent cells. More specifically, the connection unit 700 connects windows and back electrodes included in cells (C1, C2,...) Adjacent to each other.

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

  Referring to FIG. 7, a part of the buffer layer 400, the high resistance buffer layer 500, and the window layer 600 is removed to form a third through groove TH3. Accordingly, the window layer 600 is patterned to define a number of windows and a number of cells (C1, C2,...).

  As described above, according to the embodiment of the present invention, when the first through groove is formed, a phenomenon that a burr is generated due to a thermal shock by a laser can be prevented, and a solar cell with improved reliability can be obtained. Can be provided.

  In addition, the features, structures, effects, and the like described in the above embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to only one embodiment. As a result, the features, structures, effects, and the like exemplified in each embodiment can be combined or modified with respect to other embodiments by a person having ordinary knowledge in the field to which the embodiment belongs. Therefore, contents related to such combinations and modifications should be construed as being included in the scope of the present invention.

  The present invention has been described based on the preferred embodiments. However, this is merely an example, and is not intended to limit the present invention. Any person having ordinary knowledge in the field to which the present invention belongs can be used. It will be understood that various modifications and applications not described above are possible without departing from the essential characteristics of the present invention.

  For example, each component specifically shown in the embodiment can be implemented by being modified. Such differences in modification and application should be construed as being included in the scope of the present invention as defined in the appended claims.

Claims (11)

A substrate,
A back electrode layer on the substrate;
A light absorbing layer on the back electrode layer;
A buffer layer on the light absorbing layer;
A window layer on the buffer layer,
The solar cell according to claim 1, wherein the back electrode layer includes a first through groove, and the back electrode layer is formed in a trapezoidal shape having different upper and lower areas.   2. The solar cell according to claim 1, wherein a side surface of the back electrode layer in which the first through groove is formed has an inclination of 30 ° to 60 ° with respect to a vertical line of the substrate. .   The solar cell according to claim 1, wherein the back electrode layer is formed of a plurality of layers.   The solar cell according to claim 3, wherein 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 solar cell of claim 1, wherein the first through groove has a width of 20 μm to 150 μm.   The solar cell according to claim 1, further comprising a medium layer doped with sodium between the substrate and the back electrode layer. Forming a back electrode layer on the substrate;
Etching a portion of the back electrode layer to expose the top surface of the substrate;
Forming a light absorption layer, a buffer layer, and a window layer on the back electrode layer;
The step of etching a part of the back electrode layer is performed by irradiating a laser in a direction inclined with respect to the upper surface of the substrate.   The laser is irradiated a plurality of times, is symmetric with respect to a vertical line of the substrate, and is incident on the vertical line of the substrate so as to have an inclination of 30 ° to 60 °, respectively. Item 8. A method for producing a solar cell according to Item 7.   The method of manufacturing a solar cell according to claim 7, wherein the first through groove is formed by incidence of a laser having a wavelength of 500 nm to 1200 nm. The step of forming the back electrode layer includes:
Forming a lower back electrode layer adjacent to the substrate;
The method includes: forming an upper back electrode layer formed on the lower back electrode layer and having a particle density relatively higher than that of the lower back electrode layer. Solar cell manufacturing method.   9. The method of manufacturing a solar cell according to claim 8, wherein the first through-groove is formed such that the plurality of laser beams overlap with each other at 5% to 60%.

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