KR101081175B1 - 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 light absorption layer formed on the back electrode layer and including an I-II-III-VI compound; A buffer layer formed on the light absorbing layer; And a front electrode layer formed on the buffer layer. Accordingly, the electrical characteristics of the light absorbing layer can be improved.

Solar cell, 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.

In order to improve the electrical characteristics of the light absorbing layer for generating photovoltaic power in such a solar cell is being conducted.

The embodiment provides a solar cell and a method of manufacturing the same that can improve electrical characteristics of the light absorbing layer.

Solar cell according to the embodiment, the back electrode layer formed on the substrate; A light absorption layer formed on the back electrode layer and including an I-II-III-VI compound; A buffer layer formed on the light absorbing layer; And a front electrode layer formed on the buffer layer. .

According to one or more exemplary embodiments, a method of manufacturing a solar cell includes: forming a back electrode layer on a substrate; Forming a light absorbing layer including an I-II-III-VI compound on the back electrode layer; Forming a buffer layer on the light absorbing layer; And forming a front electrode layer on the buffer layer.

According to the embodiment, it is possible to artificially adjust the concentration of the hole in the light absorbing layer.

That is, the concentration of the holes in the light absorbing layer can be increased by adding a group II element to the absorbing layer made of the I-III-VI compound.

In particular, by replacing a part of the Group III element with the Group II element, the light absorbing layer including the I-II-III-VI type compound can be formed.

The concentration of holes in the light absorbing layer can be increased, and the photoelectric effect can be improved.

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

In addition, the Group II element may bond between the back electrode layer and the metal under the light absorbing layer, and an alloy film may be formed.

Therefore, the contact resistance of the back electrode layer used as the back contact of the light absorbing layer can be lowered.

In addition, it is possible to prevent the surface of the back electrode layer is damaged by the alloy layer.

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 12, a solar cell and a method of manufacturing the same will be described in detail in the embodiment.

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 may be formed in the back electrode layer 200, and the back electrode layer 200 may be separated from each other.

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 P1 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.

Referring to FIG. 3, a light absorbing layer 300 is formed on the back electrode layer 200 including the first through hole P1.

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

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

Alternatively, the light absorbing layer 300 may include a copper-zinc-indium-selenide-based compound or a copper-zinc-gallium-selenide-based compound.

According to the embodiment, zinc, which is a Group IIb element, is added to the CIGS-based light absorbing layer 300 to form a light absorbing layer 300 of the Ib-IIb-IIIb-VIb-based compound.

In the case of the general CIGS-based light absorbing layer 300, it is difficult to control the hole concentration in the light absorbing layer by the Ib-IIIb-VIb group elements.

In an embodiment, zinc, a Group IIb element, may be added to the CIGS-based light absorbing layer 300 to control the hole concentration.

This may be possible to artificially control the hole concentration in the light absorbing layer 300 by replacing a part of the Group IIIb element with the Group IIb element.

For example, the ion size (ionic size) is possible to increase the hole (hole) concentration in the light absorbing layer 300 by replacing 0.62Å of Ga ^{3 +} a Zn ^{+ 2.}

That is, the concentration of holes can be linearly increased in the light absorbing layer 300 by the number of Zn atoms replacing Ga.

For example, the concentration of holes in the light absorbing layer 300 may be artificially adjusted to be 10 ¹⁵ to 10 ¹⁷ atoms / cm 3.

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

In particular, by increasing the concentration of the hole in the light absorption layer 300 of the CISG-based compound including the Group IIb, it is possible to improve the photoelectric effect.

For example, in order to form the light absorbing layer 300, a Cu-Zn-In-Ga-based metal precursor (Cu-Zn-In-Ga-based metal precursor) is formed on the back electrode 200 using a copper target, a zinc target, an indium target, and a gallium target. precursor) film is formed.

The zinc (Zn) and gallium (Ga) may be formed on the back electrode layer 200 at a ratio of 0.1 to 0.5: 1.

That is, the Cu—Zn—In—Ga-based metal precursor film can be formed by replacing about 10 to 50% of the Group IIIb element with the Group IIb element.

Thereafter, the metal precursor film is reacted with selenium (Se) by a selenization process to form a light absorbing layer 300.

Alternatively, the light absorbing layer 300 may be formed by heating a copper, zinc, indium, gallium, selenide (Cu, Zn, In, Ga, Se) cell by co-evaporation.

Accordingly, the CISG-based light absorbing layer 300 including the group IIb may be formed on the back electrode layer 200.

4, 5 and 6 are cross-sectional views showing a method of forming the light absorbing layer by another method.

Referring to FIG. 4, a preliminary absorption layer 301 is formed on the back electrode layer 200 including the first through hole P1.

For example, the preliminary absorption layer 301 includes an Ib-IIIb-VIb-based compound.

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

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

The preliminary absorption layer 301 forms a CIG-based metal precursor film using a copper target, an indium target, and a gallium target, and reacts with selenium (Se) by a selenization process to prepare a CIGS-based preliminary layer. An absorbing layer 301 is formed.

Alternatively, the preliminary absorption layer 301 may form copper, indium, gallium, selenide (Cu, In, Ga, Se) by co-evaporation.

Referring to FIG. 5, the light absorbing layer 300 is formed on the back electrode layer 200 including the first through hole P1.

The light absorbing layer 300 may be formed by ion implanting group IIb elements into the preliminary absorbing layer 301.

For example, the group IIb element may be zinc (Zn).

Through the ion implantation process of the Group IIb element, the light absorbing layer 300 may be formed of a CISG-based compound layer including the Group IIb group.

Referring to FIG. 6, a heat treatment process may be performed on the light absorbing layer 300 to diffuse the group IIb element.

For example, the heat treatment process may be rapid thermal annealing performed at about 500 to 1500 ° C.

Through the heat treatment process, the Ib-IIb-IIIb-VIb-based compound may be strengthened in the light absorbing layer 300.

In particular, the grain size and crystallinity of the light absorbing layer 300 may be improved through the heat treatment process, and the conductivity of the light absorbing layer 300 may be improved.

7 and 8 are cross-sectional views showing a method of forming the light absorbing layer by another method. 7 is a diagram illustrating a pretreatment process for forming a light absorbing layer, and FIG. 8 is a diagram illustrating a post-treatment process for forming a light absorbing layer.

Referring to FIG. 7, an alloy layer 400 is formed on the back electrode layer 200 including the first through hole P1 by a pretreatment process.

The alloy layer 400 is an intermetallic composite.

The alloy layer 400 may be a compound of molybdenum (Mo) -IIb group element.

Alternatively, the alloy layer 400 may be formed of a Mo-IIb-Ib compound, a Mo-IIb-IIIb compound, or a Mo-IIb-Ib-IIIb compound.

Alternatively, the alloy layer 400 may be formed of a Mo-Ib compound, a Mo-IIIb compound, or a Mo-Ib-IIIb compound.

For example, the alloy layer 400 is an intermetallic composite layer formed by the intermetallic reaction of molybdenum (Mo) and zinc (Zn).

Alternatively, the alloy layer 400 may be a compound layer in which any one of zinc (Zn), copper (Cu), gallium (Ga), and indium (In) and molybdenum are combined.

For example, the alloy layer 400 may be formed on the back electrode layer 200 to have a thickness of 10 to 50 nm by sputtering or evaporation.

The alloy layer 400 may be formed along the surface of the back electrode layer 200.

In this case, the alloy layer 400 is formed by the reaction with the molybdenum thin film, which is the back electrode layer 200, and thus is not formed on the bottom surface of the first through hole P1 exposing the substrate 100. .

Referring to FIG. 8, a light absorbing layer 300 is formed on the alloy layer 400.

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

The light absorbing layer 300 may be formed by a post-treatment process.

The post-treatment process may be formed in an atmosphere containing a VIb-based element.

The pretreatment process and the aftertreatment process may be performed continuously.

For example, to form the light absorbing layer 300, a CIG-based metal precursor is formed on the back electrode layer 200 including the first through hole P1 by using a copper target, an indium target, and a gallium target. A (precursor) film is formed. In addition, a zinc target may be added to form a CZIG-based metal precursor film.

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, zinc, indium, gallium, selenide (Cu, In, Ga, Se) by co-evaporation.

Accordingly, the light absorbing layer 300 may be formed on the back electrode layer 200.

In particular, the metal layer of the selenide element constituting the light absorbing layer 300 and the molybdenum constituting the back electrode layer 200 is not formed by the alloy layer 400, thereby suppressing formation of the MoSe ₂ layer. .

The MoSe ₂ layer may interfere with the contact resistance of the back electrode layer 200 and the window layer.

The formation of MoSe ₂ may be blocked by the alloy layer 400 formed on the back electrode layer 200, and the contact resistance between the back electrode layer 200 and the window layer may be lowered.

Hereinafter, an alloy layer 400 is formed on a surface of the back electrode layer 200 to be described with reference to FIG. 8.

9, 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. 10, a second through hole P2 penetrating the high resistance buffer layer 600, the buffer layer 500, and the light absorbing layer 300 is formed.

The second through hole P2 may expose the alloy layer 400.

The second through hole P2 may be formed adjacent to the first through hole P1.

The second through hole P2 may be formed by irradiating a laser or by a mechanical method such as a tip.

Since the alloy layer 400 is formed on the back electrode layer 200, the back electrode layer 200 may be protected by a scribing process of the second through hole P2.

Referring to FIG. 11, a transparent conductive material is stacked on the high resistance buffer layer 600, and a front electrode layer 700 is formed.

When the front electrode layer 700 is formed, the transparent conductive material may be inserted into the second through hole P2 to form a connection wiring 800.

The connection wiring 800 may be electrically connected to the back electrode layer 200 through the second through hole P2.

In particular, the connection wiring 800 may be in contact with the alloy layer 400 formed on the surface of the back electrode layer 200, and may be electrically connected to the back electrode layer 200.

Accordingly, contact characteristics 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 700 is formed of zinc oxide doped with aluminum (Al) or alumina (Al ₂ O ₃ ) by a sputtering process.

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, which is the front electrode layer 700, may be formed by depositing using a ZnO target by RF sputtering, reactive sputtering by 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. 12, a third through hole P3 penetrating the front electrode layer 700, 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.

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 layer 200 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 may serve as a protective layer of the back electrode layer 200 during an etching process using the laser or the tip. Can be. Accordingly, it is possible to prevent the back electrode layer 200 from being damaged.

The light absorbing layer 300, the buffer layer 400, the high resistance buffer layer 600, and the front electrode layer 700 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 rear electrode layer 200 and the front electrode layer 700 of adjacent cells.

In an embodiment, by forming a light absorbing layer in which a group II element is added to the CIGS compound layer, the concentration of holes in the light absorbing layer may be increased.

In addition, an alloy layer may be formed on the back electrode by an additional pretreatment process before forming the light absorbing layer.

When forming the light absorbing layer by the alloy layer, it is possible to suppress the formation of MoSe ₂ , thereby improving contact characteristics of the back electrode.

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

Although described above with reference to the embodiment is only an example and is not intended to limit the invention, those of ordinary skill in the art to which the present invention does not exemplify the above within the scope not departing from the essential characteristics of this embodiment 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 12 are cross-sectional views showing a manufacturing process of the solar cell according to the embodiment.

Claims (14)

A back electrode layer formed on the substrate; A light absorption layer formed on the back electrode layer and including an I-II-III-VI compound; A buffer layer formed on the light absorbing layer; And A front electrode layer formed on the buffer layer; The concentration of holes in the light absorbing layer is 10 ¹⁵ ~ 10 ¹⁷ atom / cm 3 solar cell. The method of claim 1, The I-II-III-VI compound is any one of a copper-zinc-indium-gallium-selenide compound, a copper-zinc-gallium-selenide compound, and a copper-zinc-indium-selenide compound A solar cell that contains. The method of claim 1, The concentration ratio of the Group II element and Group III element in the light absorbing layer comprises a 0.1 to 0.5: 1. delete The method of claim 1, A solar cell formed with an alloy layer containing a group II element between the light absorbing layer and the back electrode layer. The method of claim 5, The alloy layer is a solar cell comprising an intermetallic compound layer in which at least any one of zinc, copper, gallium and indium and molybdenum is bonded. The method of claim 5, A through hole penetrating the buffer layer and the light absorbing layer and exposing the alloy layer; And a connection wiring extending from the front electrode layer and in contact with the alloy layer through the through hole. Forming a back electrode layer on the substrate; Forming a light absorbing layer including an I-II-III-VI compound on the back electrode layer; Forming a buffer layer on the light absorbing layer; And Forming a front electrode layer on the buffer layer; Forming the light absorbing layer, Depositing a Group II element on the back electrode layer and forming an alloy layer at an interface with the back electrode layer; Method of manufacturing a solar cell comprising the step of depositing an I-III-VI-based compound or I-II-III-VI-based compound on the alloy layer. The method of claim 8, The light absorbing layer is formed by depositing copper (Cu), zinc (Zn), indium (In), gallium (Ga) and selenium (Se) on the back electrode layer. delete delete The method of claim 8, The concentration ratio of the Group II element and Group III element in the light absorbing layer is a manufacturing method of a solar cell comprising 0.1 to 0.5: 1. The method of claim 8, After forming the buffer layer, forming a through hole through the light absorbing layer and the buffer layer to selectively expose the alloy layer; And the front electrode layer material is formed to fill the through hole and is connected to the alloy layer. The method of claim 8, The method of manufacturing a solar cell increases the deposition amount of the Group II element when forming the light absorbing layer, and increases the hole concentration in the light absorbing layer.

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