KR101072170B1 - Solar cell and method of fabricating the same - Google Patents

Abstract

Solar cell according to the embodiment, the back electrode formed on the substrate; A light absorbing layer formed on the back electrode; An alloy film disposed between the back electrode and the light absorbing layer and formed on a surface of the back electrode; A buffer layer formed on the light absorbing layer; A through hole exposing the back electrode through the light absorbing layer, the buffer layer and the alloy film; A recess groove formed under the through hole so that the rear electrode has a step; And a front electrode formed on the buffer layer. Therefore, the front electrode and the rear electrode directly contact with each other through the through hole, thereby improving electrical characteristics.

Solar cell, CIGS light absorption layer

Description

SOLAR CELL AND METHOD OF FABRICATING THE SAME

Embodiments relate to solar cells.

Recently, as energy demand increases, development of a solar cell converting solar energy into electrical energy is in progress.

In particular, CIGS-based solar cells that are pn heterojunction devices having a substrate structure including a glass substrate, a metal back electrode layer, a p-type CIGS-based light absorbing layer, a high resistance buffer layer, an n-type window layer, and the like are widely used.

Such a solar cell is formed by connecting a plurality of cells to each other, and researches for improving electrical characteristics of each cell are being conducted.

The embodiment provides a solar cell and a method of manufacturing the same that can improve contact characteristics of solar cells.

Solar cell according to the embodiment, the back electrode formed on the substrate; A light absorbing layer formed on the back electrode; An alloy film disposed between the back electrode and the light absorbing layer and formed on a surface of the back electrode; A buffer layer formed on the light absorbing layer; A through hole exposing the back electrode through the light absorbing layer, the buffer layer and the alloy film; A recess groove formed under the through hole so that the rear electrode has a step; And a front electrode formed on the buffer layer.

According to one or more exemplary embodiments, a method of manufacturing a solar cell includes: forming a back electrode on a substrate; Forming a light absorbing layer on the back electrode, and forming an alloy film on the surface of the back electrode by mutual reaction between the back electrode and the light absorbing layer; Forming a buffer layer on the light absorbing layer; Forming a through hole penetrating the light absorbing layer, the buffer layer, and the alloy film to expose the back electrode; Removing a portion of the back electrode on the bottom surface of the through hole to form a recess groove; And forming a front electrode on the buffer layer, wherein the front electrode material is gap-filled in the through hole and the recess groove to form a connection wiring.

According to the embodiment, it is possible to selectively remove the alloy film formed on the surface of the back electrode used as the back contact of the CIGS light absorbing layer, it is possible to improve the ohmic contact characteristics with the front electrode.

That is, when forming a through hole for forming a connection wiring extending from the front electrode, the back electrode may be exposed by removing the alloy film on the back electrode surface.

When the through hole is formed, a portion of the rear electrode may be removed to form a recess groove under the through hole.

The recess groove extends the contact area between the back electrode and the connection wiring, thereby improving electrical characteristics.

In addition, since the through hole and the recess groove are formed at the same time, the process can be simplified.

In addition, when forming a separation pattern for separating the cells through the CIGS light absorbing layer it can prevent the surface damage of the back electrode on the alloy film.

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" formed through 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 description, and does not mean a size that is actually applied.

1 to 9, a solar cell and a method of manufacturing the same will be described in detail with reference to Examples.

Referring to FIG. 1, a back electrode layer 201 is formed on a substrate 100.

The substrate 100 may be glass, and a ceramic substrate, a metal substrate, or a polymer substrate may also be used.

For example, soda lime glass (sodalime galss) or high strained soda glass (high strained point soda glass) may be used as the glass substrate. As the metal substrate, a substrate including stainless steel or titanium may be used. As the polymer substrate, polyimide may be used.

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

The back electrode layer 201 may be formed of a conductor such as metal.

For example, the back electrode layer 201 may be formed by a sputtering process using molybdenum (Mo) as a target.

This is because of the high electrical conductivity of molybdenum (Mo), ohmic bonding with the light absorbing layer, and high temperature stability under Se atmosphere.

The molybdenum thin film as the back electrode layer 201 should have a low specific resistance as an electrode and have excellent adhesion to the substrate 100 so that peeling does not occur due to a difference in thermal expansion coefficient.

For example, the back electrode layer 201 may be formed to a thickness of 1000 nm ± 100 nm, and may have a sheet resistance of about 0.3 Ω / □.

The material forming the back electrode layer 201 is not limited thereto, and may be formed of molybdenum (Mo) doped with sodium (Na) ions.

Although not shown, the back electrode layer 201 may be formed of at least one layer. When the back electrode layer 201 is formed of a plurality of layers, the layers constituting the back electrode layer 201 may be formed of different materials.

Referring to FIG. 2, a first through hole P1 is formed in the back electrode layer 201, and a plurality of back electrodes 200 is patterned.

The first through hole P1 may selectively expose the top surface of the substrate 100.

For example, the first through hole P1 may be patterned by a mechanical device or a laser device. The width of the first through hole may be 80 μm ± 20.

The back electrode 200 may be arranged in the form of a stripe or a matrix by the first through hole P1, and may correspond to each cell.

On the other hand, the back electrode 200 is not limited to the above form, it may be formed in various forms.

Referring to FIG. 3, a light absorbing layer 301 is formed on the back electrode 200 and the first through hole P1.

The light absorbing layer 301 includes an Ib-IIIb-VIb-based compound.

In more detail, the light absorbing layer 301 includes a copper-indium-gallium-selenide-based (Cu (In, Ga) Se ₂ , CIGS-based) compound.

Alternatively, the light absorbing layer 301 may include a copper-indium selenide-based (CuInSe ₂ , CIS-based) compound or a copper-gallium-selenide-based (CuGaSe ₂ , CIS-based) compound.

For example, to form the light absorbing layer 301, a CIG-based metal precursor is formed on the back electrode 200 and the first through hole P1 by using a copper target, an indium target, and a gallium target. A film is formed.

Thereafter, the metal precursor film is reacted with selenium (Se) by a selenization process to form a CIGS-based light absorbing layer 301.

In addition, the light absorbing layer 301 may form copper, indium, gallium, selenide (Cu, In, Ga, Se) by co-evaporation.

For example, the light absorbing layer 301 may be about 2000 ± 500 nm.

The light absorbing layer 301 receives external light and converts the light into electrical energy. The light absorbing layer 301 generates photo electromotive force by the photoelectric effect.

Meanwhile, when the selenization process of the light absorbing layer 301 is performed, the metal elements constituting the back electrode 200 and the elements constituting the light absorbing layer 301 may be coupled by mutual reaction. Accordingly, the alloy film 250, which is an intermetallic compound, may be formed on the surface of the back electrode 200.

For example, the alloy layer 250 may be molybdenum selenide (MoSe ₂ ), which is a compound of molybdenum (Mo) and selenide (Se).

The alloy film 250 may be formed at an interface between the light absorbing layer and the back electrode 200 to protect the surface of the back electrode 200.

Since the alloy layer 250 is not formed on the surface of the substrate 100 exposed through the first through hole P1, the light absorbing layer 301 is gapfilled in the first through hole P1. Can be.

Molybdenum selenide used as the alloy film 250 has a higher sheet resistance than the molybdenum thin film which is the back electrode 200. Therefore, in order to improve ohmic contact characteristics with the front electrode, it is required to remove the alloy film 250 on the back electrode 200 in contact with the front electrode.

Referring to FIG. 4, a buffer layer 401 and a high resistance buffer layer 501 are formed on the light absorbing layer 301.

The buffer layer 401 may be formed of at least one layer on the light absorbing layer 301, and may be formed of cadmium sulfide (CdS) by chemical bath deposition (CBD).

In this case, the buffer layer 401 is an n-type semiconductor layer, and the light absorbing layer 301 is a p-type semiconductor layer. Thus, the light absorbing layer 301 and the buffer layer 401 form a pn junction.

The high resistance buffer layer 501 may be formed as a transparent electrode layer on the buffer layer 401.

For example, the high resistance buffer layer 501 may be formed of any one of ITO, ZnO, and i-ZnO.

The high resistance buffer layer 501 may be formed of a zinc oxide layer by performing a sputtering process targeting zinc oxide (ZnO).

The buffer layer 401 and the high resistance buffer layer 501 are disposed between the light absorbing layer 301 and the front electrode to be formed later.

That is, since the difference between the lattice constant and the energy band gap is large between the light absorbing layer 301 and the front electrode, the buffer layer 401 and the high resistance buffer layer 501 having a band gap in between the two materials are inserted. A junction can be formed.

Although two buffer layers 401 are formed on the light absorbing layer 301 in this embodiment, the present invention is not limited thereto, and the buffer layer 401 may be formed as a single layer.

Referring to FIG. 5, a second through hole P2 penetrating the high resistance buffer layer 501, the buffer layer 401, the light absorbing layer 301, and the alloy film 250 is formed. The second through hole P2 may expose the back electrode 200.

In particular, when the second through hole P2 is formed, a portion of the back electrode 200 may be recessed to form a recess groove 210.

The second through hole P2 and the recess groove 210 may be formed adjacent to the first through hole P1. For example, the width of the second through hole P2 may be 80 μm ± 20 and the gap between the second through hole P2 and the first through hole P1 may be 80 μm ± 20.

Since the recess groove 210 is formed by etching a portion of the back electrode 200, the surface of the back electrode 200 under the second through hole P2 has a step. That is, the cross-sectional area of the back electrode 200 exposed by the recess groove 210 may be extended.

The alloy layer 250 may be removed by the second through hole P2 to expose the back electrode 200. In particular, since the recess groove 210 partially removes the rear electrode 200, the alloy layer 250 under the second through hole P2 may be completely removed.

The second through hole P2 and the recess groove 210 may be formed through a laser process.

Referring to FIG. 6, a transparent conductive material is stacked on the high resistance buffer layer 501, and a front electrode layer 601 is formed.

When the front electrode layer 601 is formed, the transparent conductive material may be inserted into the second through hole P2 and the recess groove 210 to form a connection wiring 700.

The connection wiring 700 may be directly connected to the rear electrode 200 through the second through hole P2. In particular, the connection wiring 700 may extend the contact area with the back electrode 200 by the recess groove 210.

Accordingly, ohmic contact between the connection line 700 and the back electrode 200 may be improved. In particular, the mobility and conductivity of the current flowing along the surface of the back electrode 200 used as a back contact of the solar cell may be improved.

The front electrode layer 601 is formed of zinc oxide doped with aluminum (Al) or alumina (Al ₂ O ₃ ) by a sputtering process.

The front electrode layer 601 is a window layer forming a pn junction with the light absorbing layer 301. Since the front electrode layer 601 functions as a transparent electrode on the front of the solar cell, zinc oxide (ZnO) having high light transmittance and good electrical conductivity is provided. Is formed.

Therefore, it is possible to form an electrode having a low resistance value by doping aluminum or alumina to the zinc oxide.

The zinc oxide thin film, which is the front electrode layer 601, may be formed by depositing using a ZnO target using RF sputtering, reactive sputtering using a Zn target, and organometallic chemical vapor deposition.

In addition, a double structure in which an indium tin oxide (ITO) thin film having excellent electro-optic properties is deposited on a zinc oxide thin film may be formed.

Referring to FIG. 7, a third through hole P3 penetrating the front electrode layer 601, the high resistance buffer layer 501, the buffer layer 401, and the light absorbing layer 301 is formed.

The third through hole P3 may selectively expose the alloy layer 250. The third through hole P3 may be formed to be adjacent to the second through hole P2.

For example, the width of the third through hole P3 may be 80 μm ± 20, and the gap between the third through hole P3 and the second through hole P2 may be 80 μm ± 20.

The third through hole P3 may be formed by irradiating a laser or by a mechanical method such as a tip.

When the third through hole P3 is formed, the surface of the back electrode may be protected by the alloy film 250.

That is, since the alloy film 250 is formed on the surface of the back electrode 200, the alloy film 250 serves as a protective layer of the back electrode 200 during an etching process using the laser or the tip. As a result, the back electrode 200 may be prevented from being damaged.

The light absorption pattern 300, the buffer pattern 400, the high resistance buffer pattern 500, and the front electrode 600, which are separated from each other by the third through hole P3, are formed. That is, the cells may be separated from each other by the third through hole P3.

In this case, each cell may be connected to each other by the connection wiring 700. That is, the connection wiring 700 may physically and electrically connect the rear electrode 200 and the front electrode 600 of adjacent cells.

By selectively removing the molybdenum selenide layer formed on the back electrode surface as described above, the ohmic contact property with the front electrode can be improved.

In addition, damage to the back electrode may be prevented by the molybdenum iselenide layer.

Accordingly, the electrical characteristics of the solar cell can be improved.

8 and 9 are cross-sectional views illustrating surfaces of the second through hole P2 and the recess groove 220 formed through the laser process in a curved shape.

As shown in FIG. 8, since the second through hole P2 is formed through a laser process, a curved groove 230 may be formed in at least one of the sidewalls of the second through hole P2. Can be.

That is, the groove 230 having a curved shape on the side surfaces of the high resistance buffer layer 501, the buffer layer 401, the light absorbing layer 301, and the alloy film 250 exposed by the sidewall of the second through hole P2. ) May be formed.

The surface area of the sidewall of the second through hole P2 may be extended by the groove 120, and then contact characteristics with the front electrode 600 may be improved.

In addition, the bottom surface of the recess groove 220 extending from the second through hole P2 may be formed in a concave curved shape.

By the curved surface of the bottom surface of the recess groove 220, the contact characteristics of the connection wiring 700 and the back electrode 200 may be improved.

The hemispherical groove 230 formed on the sidewall of the second through hole P2 and the spherical shape of the bottom of the recess groove 220 are formed by energy and wavelength of the laser process.

That is, the sidewall of the second through hole P2 and the bottom surface of the recess groove 220 may be formed in a curved shape while removing the alloy layer 250 through the laser process. In particular, the depth of the groove 230 and the recess groove 220 may be adjusted by controlling the energy and power of the laser process.

Referring to FIG. 9, a transparent conductive material is stacked on the high resistance buffer layer 501, and a front electrode layer 601 is formed.

When the front electrode layer 601 is formed, the transparent conductive material may be inserted into the second through hole P2 and the recess groove 220 to form a connection wiring 700.

Since the method of forming the front electrode layer 601 and the connection wiring 700 is the same as that of FIG. 6, a detailed description thereof will be omitted.

The connection wiring 700 may be directly connected to the rear electrode 200 through the second through hole P2.

In particular, the connection wiring 700 may improve the contact force with the second through hole P2 by the groove 230. This is because the surface area inside the second through hole P2 is increased by the groove 230.

In addition, the connection wiring 700 may have improved contact characteristics with the back electrode by the recess groove. This is because the surface area of the recess groove bottom surface is improved.

Accordingly, ohmic contact between the connection line 700 and the back electrode 200 may be improved. In particular, the mobility and conductivity of the current flowing along the surface of the back electrode 200 used as a back contact of the solar cell may be improved.

Thereafter, the process of forming the third through hole P3 illustrated in FIG. 7 may be performed.

Although the above description has been made based on the embodiments, these are merely examples and are not intended to limit the present invention. Those skilled in the art to which the present invention pertains may not have been exemplified above without departing from the essential characteristics of the present embodiments. It will be appreciated that many variations and applications are possible. For example, each component specifically shown in the embodiment can be modified. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

1 to 9 are cross-sectional views illustrating a manufacturing process of a solar cell according to an embodiment.

Claims (10)

A back electrode formed on the substrate; A light absorbing layer formed on the back electrode; An alloy film disposed between the back electrode and the light absorbing layer and formed on a surface of the back electrode; A buffer layer formed on the light absorbing layer; A through hole exposing the back electrode through the light absorbing layer, the buffer layer and the alloy film; A recess groove formed under the through hole so that the rear electrode has a step; And A front electrode formed on the buffer layer, A solar cell comprising a curved groove formed in at least one of the sidewalls of the through hole. The method of claim 1, And a connection wiring extending from the front electrode and formed inside the through hole and the recess groove. The method of claim 1, The alloy film is a molybdenum selenide (MoSe ₂ ) layer, characterized in that the solar cell. The method of claim 1, The resistance of the back electrode exposed by the recess groove is lower than the resistance of the alloy film. delete The method of claim 1, The bottom surface of the recess groove is a solar cell comprising a curved surface. Forming a back electrode on the substrate; Forming a light absorbing layer on the back electrode, and forming an alloy film on the surface of the back electrode by mutual reaction between the back electrode and the light absorbing layer; Forming a buffer layer on the light absorbing layer; Forming a through hole penetrating the light absorbing layer, the buffer layer, and the alloy film to partially expose the back electrode; Removing a portion of the back electrode on the bottom surface of the through hole to form a recess groove; And Forming a front electrode on the buffer layer, wherein the front electrode material is gap-filled in the through hole and the recess groove to form a connection wiring; The through hole and the recess groove are simultaneously formed and scribed by a laser process, and curved grooves are formed in at least one of the sidewalls of the through hole. The bottom surface of the recess groove is a method of manufacturing a solar cell comprising a curved surface. The method of claim 7, wherein The back electrode is formed of molybdenum (Mo), the light absorbing layer is formed of a copper-indium-selenide-based or copper-gallium-selenide-based compound, The method of manufacturing a solar cell of the alloy film is formed of a molybdenum selenide (MoSe ₂ ) layer through the selenization process for the light absorbing layer. delete delete

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