KR101072188B1 - Solar cell and method of fabricating the same - Google Patents

Abstract

Solar cell according to the embodiment, the back electrode layer formed on the substrate; A first through hole penetrating the back electrode layer and exposing the substrate; A first recess groove extending from the first through hole so that the substrate has a step; A light absorbing layer formed on the back electrode layer including the first through hole and the first recess groove; And a front electrode layer formed on the light absorbing layer, wherein the first recess groove is formed in a concave shape with respect to the surface of the substrate, and the bottom surface thereof has a curved surface.

Solar cell, back electrode, light absorbing 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 layer formed on the substrate; A first through hole penetrating the back electrode layer and exposing the substrate; A first recess groove extending from the first through hole so that the substrate has a step; A light absorbing layer formed on the back electrode layer including the first through hole and the first recess groove; And a front electrode layer formed on the light absorbing layer, wherein the first recess groove is formed in a concave shape with respect to the surface of the substrate, and the bottom surface thereof has a curved surface.

Solar cell according to another embodiment, the back electrode layer formed on a substrate; A light absorbing layer formed on the back electrode layer; A second through hole penetrating the light absorbing layer to expose the back electrode layer; A second through hole extending downward from the second through hole so that the rear electrode layer has a step; And a front electrode layer formed on the light absorbing layer including the second through hole, wherein the second recess groove is formed in a concave shape, and the bottom surface thereof has a curved surface.

In addition, the manufacturing method of the solar cell according to the embodiment, forming a back electrode layer on a substrate; Forming a first through hole in the back electrode layer through an isotropic etching process to selectively expose the substrate; Forming a light absorbing layer on the back electrode layer including the first through hole; Forming a buffer layer on the back electrode layer; Forming a second through hole penetrating the light absorbing layer and the buffer layer to expose the back electrode layer; And forming a front electrode layer on the buffer layer, wherein when the first through hole is formed, the substrate is selectively etched so that a first recess groove is formed under the first through hole, and the second through hole is formed. When the through hole is formed, the back electrode layer is selectively etched to form a second recess groove under the second through hole, and bottom surfaces of the first recess groove and the second recess groove have curved surfaces. Include.

According to an embodiment, the scribing process of the solar cells may be performed through an isotropic etching process using a water-jet.

That is, the first through hole separating the back electrode layer may be formed through an isotropic etching process using a water jet.

Accordingly, it is possible to prevent the phenomenon caused by the difference in the thermal expansion coefficient of the back electrode layer and the substrate, and improve the reliability of the device.

In addition, surface roughness of the sidewall of the first through hole may be improved.

In addition, when the first through hole is formed, particle generation may be minimized and electrical characteristics of the device may be improved.

The second through hole may be formed through an isotropic etching process using a water jet.

Accordingly, when forming the second through hole, the lower molybdenum selenide layer may be selectively removed, and contact characteristics with the front electrode may be improved.

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

In addition, the bottom surface of the second through hole may be formed to have a curved surface, and contact characteristics with the front electrode layer may be individualized.

In addition, the surface roughness of the sidewalls of the second through holes may be reduced, and the series resistance characteristics of the connection wirings may be improved.

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

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 the sake of explanation and does not mean the size actually applied.

1 to 10, a solar cell and a method for manufacturing the same according to an embodiment will be described in detail.

Referring to FIG. 1, a back electrode layer 200 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 200 may be formed of a conductor such as metal.

For example, the back electrode layer 200 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 200 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.

Meanwhile, the material forming the back electrode layer 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 layer 200 may be formed of at least one layer. When the back electrode layer 200 is formed of a plurality of layers, the layers constituting the back electrode layer 200 may be formed of different materials.

Referring to FIG. 2, a first through hole P1 is formed in the back electrode layer 200.

The back electrode layer 200 may be electrically and physically separated from each other by the first through hole P1.

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

The first through hole P1 may form a first recess groove 250 in the substrate 100 by partially removing the upper region of the substrate 100. The first recess groove 250 may extend from the first through hole P1.

That is, the back electrode layer 200 may be separated from each other by the first through hole P1, and the surface of the substrate 100 may be formed to have a step by the first recess groove 250. .

The first recess groove 250 may be formed concave with respect to the surface of the substrate 100, and a bottom surface thereof may have a curved surface.

The first through hole P1 may be formed through an isotropic etch process.

For example, the first through hole P1 may be formed through a wet etching process using a water jet.

That is, the back electrode layer 200 may be selectively removed by the water jet to form the first through hole P1. In this case, the substrate 100 under the first through hole P1 may also be etched to form the first recess groove 250.

In particular, since the substrate 100 is isotropically etched by the water-jet process, the bottom surface of the first recess groove 250 may have a curved surface.

In general, in the scribing process using a laser process or a tip, the rear electrode may be separated from the substrate due to a difference in thermal expansion coefficients of the substrate and the rear electrode.

In an embodiment, the first through hole P1 is formed through a wet etching process using a water jet to prevent lifting of the back electrode layer 200 separated by the first through hole P1. Can be.

In addition, the first through hole P1 may be formed through a wet etching process using the water jet, so that the sidewall of the first through hole may have a uniform shape.

In addition, referring to FIG. 3, when the water-jet process time is extended, the etchant is isotropically etched while the etchant penetrates in the lateral direction (x, x ′) of the substrate 100.

Accordingly, the first recess groove 250 has a wider width than the first through hole P1.

That is, the width of the first through hole P1 is formed to be the first width w1, and the width of the first recess groove 250 is the second width w2 wider than the first width w1. It can be formed as.

For example, the width of the first through hole P1 may be 60 μm ± 20, and the width of the first recess groove 250 may be 80 μm ± 20.

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

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

Thereafter, the back electrode layer 200 and the first through hole P1 may be cleaned and dried.

Since the first through hole P1 is formed through an isotropic etching process using a water jet, it is possible to suppress the generation of residues such as particles that may be generated during the etching process of the back electrode layer 200.

That is, since the first through hole P1 is formed through the water-jet process, the residue of the rear electrode layer 200 may be minimized, and the residue may be removed by using the water-jet.

Accordingly, it is possible to prevent the back electrode layers 200 adjacent to each other from being short-circuited.

Referring to FIG. 4, the light absorbing layer 300 is formed on the back electrode layer 200 and the first through hole P1.

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, to form the light absorbing layer 300, a CIG-based metal precursor is formed on the back electrode layer 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 300.

In addition, the light absorbing layer 300 may form copper, indium, gallium, selenide (Cu, In, Ga, Se) by co-evaporation.

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.

Meanwhile, when the selenization process of the light absorbing layer 300 is performed, the metal elements constituting the back electrode layer 200 and the elements constituting the light absorbing layer 300 may be coupled by mutual reaction. Accordingly, an alloy layer 400, which is an intermetallic composite, may be formed on the surface of the back electrode layer 200.

For example, the alloy layer 400 may be molybdenum selenide (MoSe ₂ ), which is a compound of molybdenum (Mo) and selenide (Se).

The alloy layer 400 may be formed at an interface between the light absorbing layer 300 and the back electrode layer 200 to protect the surface of the back electrode layer 200.

Since the alloy layer 400 is not formed on the surface of the substrate 100 exposed through the first through hole P1, the light absorption layer 300 is gapfilled in the first through hole P1. Can be.

The molybdenum selenide layer as the alloy layer 400 has a higher sheet resistance than the molybdenum thin film as the back electrode layer 200. Therefore, since the contact resistance of the back electrode layer 200 is increased, removal is required.

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 layer on the light absorbing layer 300. The buffer layer 500 may be formed of cadmium sulfide (CdS) by chemical bath deposition (CBD).

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

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 high resistance buffer layer 600 may be formed of a zinc oxide layer by performing a sputtering process targeting zinc oxide (ZnO).

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

That is, since the difference between the lattice constant and the energy band gap between the light absorbing layer 300 and the front electrode is large, the buffer layer 500 and the high resistance buffer layer 600 having a band gap in between the two materials are inserted into a good one. A junction can be formed.

Although two buffer layers 500 are formed on the light absorbing layer 300 in this embodiment, the present invention is not limited thereto, and the buffer layer 500 may be formed as a single layer.

Referring to FIG. 6, a second through hole P2 penetrating the high resistance buffer layer 600, the buffer layer 500, the light absorbing layer 300, and the alloy layer 400 is formed.

The second through hole P2 may expose the back electrode layer 200.

When the second through hole P2 is formed, a portion of the upper region of the back electrode layer 200 may be removed and a second recess groove 650 may be formed in the back electrode layer 200.

That is, the second recess groove 650 may be formed by recessing the surface of the back electrode layer 200. The second recess groove 650 may extend from the second through hole P2.

The light absorbing layer 300 and the buffer layer 500 are separated from each other by the first through hole P1, and the surface of the back electrode layer 200 is exposed by the second recess groove 650, and a step is removed. Can have

The second recess groove 650 may be formed in a concave shape with respect to the surface of the back electrode layer 200, and a bottom surface thereof may have a curved surface.

The cross-sectional area of the back electrode layer 200 exposed by the second recess groove 650 may be extended.

The alloy layer 400 may be removed by the second through hole P2 to expose the back electrode layer 200.

In particular, since the second recess groove 650 removes a part of the back electrode layer 200, the alloy layer 400 under the second through hole P2 may be completely removed.

The second through hole P2 and the second recess groove 650 may be formed through an isotropic etching process. That is, the second through hole P2 and the second recess groove 650 may be formed through a wet etching process using a water jet.

 The water-jet process for forming the second through hole P2 and the second recess groove 650 is the same as the method for forming the first through hole P1 and the first recess groove 250. Detailed description thereof will be omitted.

Since the back electrode layer 200 is etched isotropically through an isotropic etching process using the water-jet, the bottom surface of the second recess groove 650 may have a curved surface.

In general, the sidewall of the second through hole is non-uniform, i.e., the sidewall of the second through hole becomes rough in a scribing process using a laser process or a tip, causing roughness and causing a shunt path. You can.

In an embodiment, the second through hole P2 may be formed through a scribing process using a water jet, and the roughness of the sidewalls of the second through hole P2 may be reduced.

In addition, referring to FIG. 7, when the water-jet process time is extended, an etchant penetrates in the lateral direction (x−x ′) of the back electrode layer 200 and the back electrode layer 200 may be etched isotropically. .

Accordingly, the second recess groove 650 has a wider width than the second through hole P2. That is, the width of the second through hole P2 is formed as the third width w3, and the width of the second recess groove 650 is the fourth width w4 wider than the third width w3. Can be formed.

For example, the width of the second through hole P2 may be 60 μm ± 20 μm, and the width of the second recess groove 650 may be 80 μm ± 20 μm.

In addition, the second through hole P2 may be formed to be adjacent to the first through hole P1. For example, the gap between the first through hole P1 and the second through hole P2 may be 60 μm ± 20 μm.

Thereafter, a cleaning and drying process may be performed on the substrate 100 including the second through hole P2.

The alloy layer 400 may be selectively removed by the second through hole P2 and the second recess groove 650 to expose the back electrode layer 200.

Therefore, the contact characteristics of the back electrode layer 200 may be improved.

Referring to FIG. 8, a transparent conductive material is stacked on the high resistance buffer layer 600, and a front electrode layer 800 is formed.

When the front electrode layer 800 is formed, the transparent conductive material may be inserted into the second through hole P2 and the second recess groove 650 to form a connection wiring 800.

The connection wiring 800 may be directly connected to the back electrode layer 200 through the second through hole P2. In particular, the connection wiring 800 may extend the contact area with the back electrode layer 200 by the second recess groove 650.

Accordingly, ohmic contact between the connection wiring 800 and the back electrode layer 200 may be improved. In particular, the mobility and conductivity of the current flowing along the surface of the back electrode layer 200 used as a back contact of the solar cell may be improved.

The front electrode layer 800 is formed of zinc oxide doped with aluminum (Al) or alumina (Al ₂ O ₃ ) through a sputtering process.

The front electrode layer 800 is a window layer forming a pn junction with the light absorbing layer 300. Since the front electrode layer 800 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 800, may be formed by 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 tin oxide (ITO) thin film having excellent electro-optic properties is deposited on a zinc oxide thin film may be formed.

Referring to FIG. 9, a third through hole P3 penetrating the front electrode layer 800, the high resistance buffer layer 600, the buffer layer 500, and the light absorbing layer 300 is formed.

The third through hole P3 may selectively expose the alloy layer 400. 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 60 μm ± 20 and the gap between the third through hole P3 and the second through hole P2 may be 60 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 layer 400.

That is, since the alloy layer 400 is formed on the surface of the back electrode layer 200, the alloy layer 400 serves as a protective layer of the back electrode layer 200 during an etching process using the laser or the tip. As a result, the back electrode layer 200 may be prevented from being damaged.

The light absorbing layer 300, the buffer layer 500, the high resistance buffer layer 600, and the front electrode layer 800 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 800. That is, the connection wiring 800 may physically and electrically connect the back electrode layer 200 and the front electrode layer 800 of adjacent cells.

FIG. 10 illustrates that a first recess groove 250 extending below the first through hole P1 is formed as a second width w2 and a second extending below the second through hole P2. The recess groove 650 is formed to have a fourth width w4.

In an embodiment, the first through hole and the second through hole may be formed through an isotropic etching process using a water jet.

Accordingly, it is possible to prevent the back electrode layer and the substrate from being lifted in the first through hole, and to prevent a defect of the device.

In addition, when forming the second through hole, the lower molybdenum selenide layer may be selectively removed to improve contact characteristics with the front electrode.

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

In addition, residues generated when the first through hole and the second through hole are formed may be removed, and leakage current may be prevented.

Accordingly, 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 10 are cross-sectional views showing a manufacturing process of a solar cell according to the embodiment.

Claims (12)

A back electrode layer formed on the substrate; A first through hole penetrating the back electrode layer and exposing the substrate; A first recess groove extending from the first through hole so that the substrate has a step, and in contact with the substrate; A light absorbing layer formed on the back electrode layer including the first through hole and the first recess groove; And A front electrode layer formed on the light absorbing layer; The first recess groove is formed in a concave shape with respect to the surface of the substrate, the bottom surface of the solar cell comprising a curved surface. The method of claim 1, The width of the first through hole is formed in a first width, the width of the first recess groove is formed in a second width wider than the first width. delete A back electrode layer formed on the substrate; A light absorbing layer formed on the back electrode layer; A second through hole penetrating the light absorbing layer to expose the back electrode layer; A second recess groove extending downward from the second through hole so that the back electrode layer has a step, and in contact with the back electrode layer; A front electrode layer formed on the light absorbing layer including the second through hole, The second recess groove is formed in a concave shape, the bottom surface of the solar cell comprising a curved surface. 5. The method of claim 4, Further comprising an alloy layer formed at the interface between the back electrode layer and the light absorbing layer, The alloy layer is a molybdenum selenide (MoSe ₂ ) layer, characterized in that the solar cell. The method of claim 5, The width of the second through hole is formed in a third width, the width of the second recess groove is formed in a fourth width wider than the third width. 5. The method of claim 4, And a connection wiring extending from the front electrode layer and directly contacting the rear electrode layer through the second through hole. Forming a back electrode layer on the substrate; Forming a first through hole in the back electrode layer through an isotropic etching process to selectively expose the substrate; Forming a light absorbing layer on the back electrode layer including the first through hole; Forming a buffer layer on the back electrode layer; Forming a second through hole penetrating the light absorbing layer and the buffer layer to expose the back electrode layer; And Forming a front electrode layer on the buffer layer; When the first through hole is formed, the substrate is selectively etched to form a first recess groove in contact with the substrate under the first through hole. When forming the second through hole, the back electrode layer is selectively etched to form a second recess groove in contact with the back electrode layer under the second through hole. The bottom surface of the first recess groove and the second recess groove is a manufacturing method of a solar cell comprising a curved surface. The method of claim 8, The first through hole including the first recessed groove and the second through hole including the second recessed groove are formed in a water-jet process. The method of claim 8, A width of the first through hole and the second through hole is formed to a first width, the width of the first recess groove and the second recess groove is formed in a second width wider than the first width Way. The method of claim 8, As the time of the isotropic etching process for the first through hole and the second through hole is extended, the width of the first recess groove and the second recess groove becomes wider than the width of the first through hole. . The method of claim 8, When the light absorbing layer is formed, an alloy layer, which is an intermetallic compound layer, is formed at an interface between the light absorbing layer and the back electrode layer, And the alloy layer is selectively removed by the second through hole and the second recess groove.

Images