KR20110047724A - Solar cell and mehtod of fabricating the same - Google Patents

Abstract

PURPOSE: A solar cell and a manufacturing method thereof are provided to improve a contact property by directly contacting a front electrode and a rear electrode through a second penetration hole. CONSTITUTION: A rear electrode layer(200) is formed on a substrate and is divided by a first penetration hole. A first mask pattern has the first penetration hole and a first gap and is formed on the rear electrode layer. A second mask pattern has the first mask pattern and a second gap and is formed on the rear electrode layer. A light absorbing layer is formed on the rear electrode and is lower than the first mask pattern and the second mask pattern. A buffer layer(500) is formed on the light absorbing layer and is lower than the first mask pattern and the second mask pattern. A second penetration hole is formed by removing the first mask pattern. A front electrode layer(700) is formed on the buffer layer including the second penetration hole.

Description

SOLAR CELL 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, CIGS-based solar cells, which are pn heterojunction devices of a substrate structure, including a glass substrate, a metal back electrode layer, a p-type CIGS-based light absorbing layer, a buffer layer, an n-type window layer, and the like are used.

In order to form such a solar cell, a mechanical patterning process may be performed.

When the mechanical patterning process is performed, precise patterning is difficult, and defects such as adding a buffer width may occur during patterning. In addition, particles or the like may remain due to laser or mechanical patterning, thereby increasing the series resistance.

This increases the dead zone area of the solar cell and may cause a decrease in light efficiency.

The embodiment provides a solar cell and a method of manufacturing the same, which can form a uniform pattern to reduce a dead zone area and improve efficiency.

A solar cell according to an embodiment includes: a back electrode formed on a substrate and separated from each other by a first through hole; A first mask pattern formed on the back electrode to have the first through hole and the first gap; A second mask pattern formed on the back electrode to have a second gap with the first mask pattern; A light absorbing layer formed on the back electrode including the first through hole and formed at a lower height than the first mask pattern and the second mask pattern; A buffer layer formed on the light absorbing layer and formed at a height lower than that of the first and second mask patterns; A second through hole formed by removing the first mask pattern; And a front electrode formed on the buffer layer including the second through hole.

A method of manufacturing a solar cell according to an embodiment includes forming a back electrode separated by a first through hole on a substrate; Forming a first mask pattern having the first through hole and the first gap and a second mask pattern having the first mask pattern and the second gap on the back electrode; Forming a light absorbing layer formed on a rear electrode including the first through hole and exposing surfaces of the first and second mask patterns; Forming a buffer layer formed on the light absorbing layer and exposing surfaces of the first and second mask patterns; Removing the first mask pattern and forming a second through hole to expose the back electrode; And forming a front electrode on the buffer layer including the second through hole.

According to the embodiment, the contact characteristics of the rear electrode and the front electrode can be improved.

This may form first and second mask patterns on the back electrode before forming the CIGS light absorbing layer, and may not selectively form an alloy film at an interface of the back electrode.

Thereafter, a front electrode may be formed in the through hole formed by removing the first mask pattern.

Accordingly, the front electrode may be directly connected to the rear electrode and may improve electrical contact characteristics of the solar cell.

The solar cell according to the embodiment may be applied to various substrates, that is, hard or flexible substrates.

This is because the light absorbing layer is formed through the electroplating process proceeds at a low temperature, it is possible to use a low hardness or flexible substrate.

As a result, the solar cell can be reduced in weight and size.

In addition, since the second through hole and the third through hole are formed by the second and third mask patterns, a separate scribing process may be omitted.

In particular, since the pattern nonuniformity caused by the scribing process can be prevented, the electrical characteristics of the solar cell can be improved.

In the description of the embodiments, each substrate, layer, film, crystal, or electrode is described as being formed "on" or "under" of each substrate, layer, film, crystal, or electrode. In the case, “on” and “under” include both being formed “directly” or “indirectly” 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 the sake of explanation and does not mean the size actually applied.

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

Referring to FIG. 1, a plurality of back electrodes 200 are 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 or 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 200 forms a back electrode layer (not shown) on the substrate 100 and selectively patterns the back electrode layer defined as the first through hole predetermined region P1 to correspond to each cell. The first through hole 250 may be formed.

That is, the back electrodes 200 may be separated from each other by the first through hole 250. The first through hole 250 may selectively expose the top surface of the substrate 100.

For example, the first through hole 250 may be formed by a mechanical device or a laser device. The width of the first through hole 250 may be 80 ± 20 μm.

The back electrode 200 may be formed of a conductor such as metal.

For example, the back electrode 200 may be formed by a sputtering process using molybdenum (Mo) as a target.

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

The molybdenum (Mo) thin film, which is the back electrode 200, must 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.

The material forming the back electrode 200 is not limited thereto, and may be formed of molybdenum (Mo) doped with sodium (Na) ions.

Although not shown in the drawing, the back electrode 200 may be formed of at least one layer. When the back electrode 200 is formed of a plurality of layers, the layers constituting the back electrode 200 may be formed of different materials.

Referring to FIG. 2, a first mask pattern 10 and a second mask pattern 20 are formed on the back electrode 200.

The first mask pattern 10 may be formed in the second through hole predetermined region P2. The second mask pattern 20 may be formed in the third through hole predetermined region P3.

For example, the widths of the first mask pattern 10 and the second mask pattern 20 may be 80 ± 20 μm.

The first mask pattern 10 may be formed to be adjacent to the first through hole 250. For example, the first mask pattern 10 may be formed to have the first through hole 250 and the first gap G1.

The second mask pattern 20 may be formed adjacent to the first mask pattern 10. For example, the second mask pattern 20 and the first mask pattern 10 may be formed to have a second gap G2.

For example, the widths of the first gap G1 and the second gap G2 may be 80 ± 20 μm.

The first and second mask patterns 20 and 30 may have the same height or different heights.

For example, the first mask pattern 10 may be formed to have a first height H1, and the second mask pattern 20 may be formed to have a second height H2 that is higher than the first height H1. have. The first mask pattern 10 and the second mask pattern 20 may have a height of 1 μm to 5 μm.

The first and second mask patterns 20 and 30 may be formed of a thermosetting or photocurable resin. Alternatively, the first and second mask patterns 20 and 30 may be formed of an insulating material such as an oxide film or a nitride film.

For example, the first and second mask patterns 20 and 30 may be formed of a material such as a photoresist material or a resin.

The first and second mask patterns 20 and 30 may be formed by spin coating a photoresist layer on the substrate 100 including the back electrode 200. An exposure mask (not shown) defining second and third through hole predetermined regions P2 and P3 is positioned on the photoresist film. The first and second mask patterns 20 and 30 may be formed by performing an exposure and development process using the exposure mask. In this case, the first mask pattern 10 and the second mask pattern 20 may be simultaneously formed.

Alternatively, as shown in FIG. 3, the first mask pattern 10 is formed by a photolithography process using a positive type photoresist, and the second mask pattern 20 forms a negative photoresist. It can form by the used photolithography process.

That is, when exposed to light or radiation, only a part of the structure changes, and a negative type that does not dissolve in a solvent and vice versa, which is easily melted, is used, respectively, so that the first mask pattern 10 and the second mask having different characteristics are different. The pattern 20 can be formed.

Referring to FIG. 4, the light absorbing layer 300 is formed on the back electrode 200 including the first through hole 250.

The light absorbing layer 300 may be formed at a height lower than that of the first and second mask patterns 20 and 30. That is, the first mask pattern 10 and the second mask pattern 20 may have a shape protruding from an upper surface of the light absorbing layer 300.

The light absorbing layer 300 includes an Ib-IIIb-VIb-based compound.

In more detail, the light absorbing layer 300 includes a copper-indium-gallium-selenide-based (Cu (In, Ga) Se ₂ , CIGS-based) compound.

Alternatively, the light absorbing layer 300 may include a copper-indium selenide-based (CuInSe ₂ , CIS-based) compound or a copper-gallium-selenide-based (CuGaSe ₂ , CGS-based) compound.

For example, the light absorbing layer 300 may be formed through an electroplating process.

When the light absorbing layer 300 is formed, a molybdenum (Mo) or copper (Cu) film may be first formed as a seed film, followed by an electroplating process. Alternatively, since the back electrode 200 may be used as a seed film, the seed film may not be formed.

The temperature during the electroplating process may be maintained at 10 ~ 200 ℃.

The electroplating process may be performed using MeTal-Cl, Se-Oxide and DI as a solution, or using MeTal-Cl, SeCl and Dl as a solution. The pH of the solution may be 1-5.

Metal used in the electroplating process may be a group I and group element such as copper (Cu), indium (In), gallium (Ga).

By the electroplating process, the light absorbing layer 300 may be uniformly deposited on the back electrode 200 including the first through hole 250 at a high density. In particular, the light absorbing layer 300 may be deposited without voids in the first gap G1 and the second gap G2, which are areas between the first mask pattern 10 and the second mask pattern 20.

The light absorbing layer 300 is formed on the back electrode 200 except for the first mask pattern 10 and the second mask pattern 20.

In this case, an alloy film formed of MoSe ₂ along the surface of the back electrode 200 corresponding to the remaining area except for the region where the first and second mask patterns 20 and 30 and the back electrode 200 are connected ( 400) can be formed.

That is, when the light absorbing layer 300 is formed, a MoSe ₂ layer may be formed on the surface of the back electrode 200 by chemically bonding the molybdenum film and selenium. In this case, since the first and second mask patterns 20 and 30 are formed on the surface of the back electrode 200 corresponding to the second and third through hole predetermined regions P2 and P3, the MoSe ₂ alloy layer is formed. 400 is not formed.

Since the light absorbing layer 300 is formed through the electroplating process, which is a low temperature process, in some embodiments, the flexible substrate 100 may be applied.

The light absorbing layer 300 receives external light and converts the light into electrical energy. The light absorbing layer 300 generates photo electromotive force by the photoelectric effect.

In general, a through hole is formed through a scribing process to penetrate the light absorbing layer to connect the front electrode and the rear electrode of the unit cell. In addition, patterning for separating the unit cells is also formed through a scribing process. However, the pattern of the through hole by this scribing process may be formed non-uniformly to increase the dead zone area. In addition, since the removal of MoSe ₂ formed at the interface between the back electrode 200 and the light absorbing layer 300 is not easy, there is a problem that the contact resistance is increased.

In an embodiment, the first and second mask patterns 20 and 30 are first formed on the rear electrode 200 in the second and third through hole predetermined regions P2 and P3, and then the light absorbing layer 300 is formed. Since it is formed, a separate scribing process can be omitted. In addition, since MoSe ₂ is not formed in the second and third through hole predetermined regions P2 and P3, contact characteristics between the front electrode and the rear electrode 200 may be improved.

Referring to FIG. 5, a buffer layer 500 and a high resistance buffer layer 600 are formed on the light absorbing layer 300.

The buffer layer 500 may be formed of at least one or more layers on the light absorbing layer 300, and may be formed by stacking cadmium sulfide (CdS).

In this case, the buffer layer 500 is an n-type semiconductor layer, the light absorbing layer 300 is a p-type semiconductor layer. Accordingly, the light absorbing layer 300 and the buffer layer 500 form a pn junction.

The high resistance buffer layer 600 may be sputtered to target zinc oxide (ZnO) to further form a zinc oxide layer on the cadmium sulfide (CdS).

The high resistance buffer layer 600 may be formed as a transparent electrode layer on the buffer layer 500.

For example, the high resistance buffer layer 600 may be formed of any one of ITO, ZnO, and i-ZnO.

The buffer layer 500 and the high resistance buffer layer 600 may be formed to have a lower height than the first and second mask patterns 20 and 30. That is, the first mask pattern 10 and the second mask pattern 20 may have a shape protruding from an upper surface of the buffer layer 500.

Alternatively, the high resistance buffer layer 600 may be formed at the same height as the first mask pattern 10, and an upper surface of the first mask pattern 10 may be exposed to an upper portion of the high resistance buffer layer 600.

The buffer layer 500 and the high resistance buffer layer 600 are disposed between the light absorbing layer 300 and the front electrode formed thereafter.

That is, since the difference between the lattice constant and the energy band gap is large between the light absorbing layer 300 and the front electrode layer, a good junction is formed by inserting the buffer layer 500 and the high resistance buffer layer having a band gap between the two materials. can do.

In the present exemplary embodiment, two buffer layers 500 are formed on the light absorbing layer 300. However, the present invention is not limited thereto, and the buffer layer 500 may be formed of only one layer.

Referring to FIG. 6, the first mask pattern 10 is removed and a second through hole 650 is formed.

Since the first mask pattern 10 is formed on the rear electrode 200 through the high resistance buffer layer 600, the buffer layer 500, and the light absorbing layer 300, the first mask pattern 10 is formed. The second through hole 650 may be formed by selective removal of the second through hole 650.

The second through hole 650 may selectively expose the back electrode 200. The second through hole 650 may be formed to have the first through hole 250 and the first gap G1.

Since MoSe ₂ is not formed on the surface of the rear electrode 200 in the first mask pattern 10, the second through hole 650 may directly expose the upper surface of the rear electrode 200. .

Referring to FIG. 7, the front electrode layer 700 is formed by stacking a transparent conductive material on the high resistance buffer layer 600 including the second through hole 650.

When the front electrode layer 700 is formed, the transparent conductive material may be inserted into the second through hole 650 to form a connection wiring 800.

The front electrode layer 700 is formed of zinc oxide doped with aluminum (Al) or alumina (Al ₂ O ₃ ) by a sputtering process.

For example, the front electrode layer 700 may be formed to a thickness of 800nm ± 100.

The front electrode layer 700 is a window layer forming a pn junction with the light absorbing layer 300. Since the front electrode layer functions as a transparent electrode on the front of a 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 as the front electrode layer 700 may be formed by a method of depositing using a ZnO target by RF sputtering, reactive sputtering using a Zn target, and organometallic chemical vapor deposition.

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

The front electrode layer 700 may be formed at a height lower than that of the second mask pattern 20. That is, the second mask pattern 20 may have a shape protruding from the top surface of the front electrode layer 700.

Each cell may be connected to each other by the connection wiring 800. That is, the connection wiring 800 may physically and electrically connect the rear electrode 200 and the front electrode layer 700 of adjacent cells.

In particular, the connection wiring 800 may directly contact the back electrode 200 through the second through hole 650. Accordingly, the contact characteristics of the connection wiring 800 and the back electrode 200 can be improved.

Since the third mask pattern 20 is formed in the third through hole plan region P3, the cells may be in a separated state.

Meanwhile, when forming the front electrode layer 700, the transparent electrode material 710 may remain on the surface of the second mask pattern 20.

Therefore, as illustrated in FIG. 8, the transparent electrode material 710 on the surface of the second mask pattern 20 may be selectively removed through a dry etching process using plasma.

In addition, as shown in FIG. 9, the second mask pattern 20 may be removed and the third through hole 750 may be exposed.

Since the second mask pattern 20 is made of a transparent material, it may not be removed.

As described above, since MoSe ₂ is not formed on the rear electrodes corresponding to the second and third through holes, contact characteristics between the rear electrodes and the front electrodes may be improved.

In addition, since the light absorbing layer is formed through the electroplating process proceeds at a low temperature, the embodiment can use a low hardness or a flexible substrate. As a result, the solar cell can be reduced in weight.

In addition, since the second through hole and the third through hole are formed by the second and third mask patterns, a separate scribing process may be omitted.

In particular, since the pattern nonuniformity caused by the scribing process can be prevented, the electrical characteristics of the solar cell can be improved.

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 showing a method of manufacturing a solar cell according to the embodiment.

Claims (10)

A back electrode formed on the substrate and separated from each other by the first through hole; A first mask pattern formed on the back electrode to have the first through hole and the first gap; A second mask pattern formed on the back electrode to have a second gap with the first mask pattern; A light absorbing layer formed on the back electrode including the first through hole and formed at a lower height than the first mask pattern and the second mask pattern; A buffer layer formed on the light absorbing layer and formed at a height lower than that of the first and second mask patterns; A second through hole formed by removing the first mask pattern; And A solar cell comprising a front electrode formed on the buffer layer including the second through hole. The method of claim 1, The first mask pattern and the second mask pattern are formed of an insulating material solar cell. The method of claim 1, The first mask pattern and the second mask pattern is a solar cell formed of a thermosetting resin or photocurable resin. The method of claim 1, A solar cell comprising an alloy film selectively formed only at an interface between the back electrode and the light absorbing layer. The method of claim 1, The front electrode is in direct contact with the surface of the back electrode through the second through hole. Forming a back electrode separated by a first through hole on the substrate; Forming a first mask pattern having the first through hole and the first gap and a second mask pattern having the first mask pattern and the second gap on the back electrode; Forming a light absorbing layer formed on a rear electrode including the first through hole and exposing surfaces of the first and second mask patterns; Forming a buffer layer formed on the light absorbing layer and exposing surfaces of the first and second mask patterns; Removing the first mask pattern and forming a second through hole to expose the back electrode; And A method of manufacturing a solar cell comprising forming a front electrode on a buffer layer including the second through hole. The method of claim 6, The first mask pattern and the second mask pattern is a method of manufacturing a solar cell formed of a photocurable or thermosetting resin. The method of claim 6, Forming the first mask pattern and the second mask pattern, Coating a photoresist film on the substrate including the back electrode; And A method of manufacturing a solar cell comprising forming through a selective exposure process to the photoresist film. The method of claim 6, The light absorbing layer is a manufacturing method of a solar cell comprising forming through an electroplating (Electro plating). The method of claim 6, Forming the front electrode layer, Depositing a transparent electrode material on the buffer layer including the second mask pattern so that the second through hole is gap-filled; And And selectively removing the transparent electrode material formed on the surface of the second mask pattern by a plasma treatment process.

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