KR101063699B1 - Solar cell and manufacturing method thereof - Google Patents

Abstract

A solar cell is disclosed. The solar cell according to the embodiment includes a back electrode formed on the substrate; A nitride semiconductor layer formed on the back electrode; A light absorbing layer formed on the nitride semiconductor layer; And a front electrode formed on the light absorbing layer. The nitride semiconductor layer may improve the light efficiency of the light absorbing layer by reflecting incident light to the light absorbing layer.

Solar cell, CIGS

Description

SOLAR CELL AND METHOD OF FABRICATING THE SAME

Embodiments relate to solar cells.

Recently, as the demand for energy increases, development of solar cells for converting solar energy into electrical energy is in progress.

In particular, a CIGS solar cell which is a pn heterojunction device 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 is widely used.

In order to improve the performance of such a solar cell, studies are being conducted to improve the light receiving efficiency.

The embodiment provides a solar cell and a method of manufacturing the same that can increase light efficiency.

Solar cell according to the embodiment, the back electrode formed on the substrate; A nitride semiconductor layer formed on the back electrode; A light absorbing layer formed on the nitride semiconductor layer; And a front electrode formed on the light absorbing layer.

A method of manufacturing a solar cell according to the embodiment includes forming a back electrode on a substrate; Forming a nitride semiconductor layer on the back electrode; Forming a light absorbing layer on the nitride semiconductor layer; And forming a front electrode on the light absorbing layer.

A solar cell and a method of manufacturing the same according to the embodiment include a nitride semiconductor layer that is a reflective layer under the light absorbing layer. Thereby, the light absorption rate of the said light absorption layer can be improved.

In particular, a plurality of protrusions are formed on the surface of the nitride semiconductor layer to increase the reflectance to the light absorbing layer and improve the light efficiency of the solar cell.

In addition, the light absorbing layer may have an improved light efficiency with a minimum thickness by the nitride semiconductor layer.

That is, since the light path of the incident light is more than doubled by the nitride semiconductor layer, the absorption rate of the light absorbing layer can be improved.

Accordingly, by reducing the thickness of the light absorbing layer, it is possible to reduce material costs and improve productivity.

The nitride semiconductor layer includes a nitride film doped with p-type impurities. Therefore, it may have good interfacial properties with respect to the light absorbing layer.

Since the nitride semiconductor layer can be formed by MOCVD, damage to the underlying film can be prevented.

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.

7 is a cross-sectional view showing a solar cell according to an embodiment. 8 is a perspective view of FIG. 7.

The solar cell according to the embodiment includes a back electrode 110 formed on the substrate 100, a nitride semiconductor layer 120 formed on the back electrode 110, and light formed on the nitride semiconductor layer 120. An absorbing layer 130 and a front electrode 160 formed on the light absorbing layer 130.

A buffer layer 140 and a high resistance buffer layer 150 may be disposed between the light absorbing layer 130 and the front electrode 160. Therefore, the light absorbing layer 130 and the front electrode 160 can form a good junction.

A plurality of protrusions 125 are formed on the surface of the nitride semiconductor layer 120. The protrusion 125 may be formed in a pyramid or cone shape.

The nitride semiconductor layer 120 may be formed of any one of GaN, AlN, InN (AlGa) N, (InGa) N, (AlIn) N, and (AlGaIn) N.

The nitride semiconductor layer 120 may be a nitride film doped with p-type impurities. For example, the p-type impurity may be magnesium (Mg).

The nitride semiconductor layer 120 may act as a reflective film of incident light and increase the light absorption rate of the light absorbing layer 130.

This is because light passing through the light absorbing layer 130 may be reflected back to the light absorbing layer 120 by the nitride semiconductor layer 120. Accordingly, the light absorption rate of the light absorption layer 130 may be increased.

The nitride semiconductor layer 120 may be formed of a p-type impurity, and the light absorbing layer 130 may also be formed of a p-type impurity, thereby providing good interface characteristics.

The thickness of the back electrode 110 and the light absorbing layer 130 may have a ratio of 1: 1 to 1.5. For example, the light absorbing layer 130 may have a thickness of 1000 nm to 1500 nm.

This is because the light path of the incident light is increased by more than twice by the nitride semiconductor layer 120, even if the light absorbing layer 130 has a small thickness can be improved light absorption.

1 to 8 illustrate a method of manufacturing a solar cell according to an embodiment.

Referring to FIG. 1, a back electrode 110 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 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 may be rigid or flexible.

The back electrode 110 may be formed of a conductor such as metal.

The back electrode 110 is formed of a metal to improve the series resistance characteristics, it is possible to increase the electrical conductivity. For example, the back electrode 110 may be formed to a thickness of 500 ~ 1500nm.

For example, the back electrode 110 may be formed by a sputtering process using molybdenum (Mo) as a target.

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

The molybdenum thin film, which is the back electrode 110, 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.

The material forming the back electrode 110 is not limited thereto, and may be formed of molybdenum (Mo) doped with indium tin oxide (ITO) and sodium (Na) ions.

The back electrode 110 may be formed of at least one layer.

For example, the back electrode 110 may be formed to a thickness of about 1000 nm by DC sputtering targeting molybdenum (Mo).

In this case, a thickness of 300 to 500 nm, which is the initial film of the rear electrode 110, may be grown at low power and high pressure. In addition, the thickness of the 500-700 nm of the back electrode 110 may be formed at high power and low pressure.

Accordingly, the back electrode 110 may be formed of two layers having different crystal densities, and may improve adhesion and conductivity.

When the back electrode 110 is formed of a plurality of layers, the layers constituting the back electrode 110 may be formed of different materials.

2 to 4, the nitride semiconductor layer 120 is formed on the back electrode 110.

The nitride semiconductor layer 120 may be a reflective film that reflects incident light.

The nitride semiconductor layer 120 may be formed of a p-type doped Nitride layer doped with p-type impurities. For example, the carrier concentration of the nitride semiconductor layer 120 may be 1 × 10 ¹⁶ to 1 × 10 ¹⁹ atom / cm 2.

The nitride semiconductor layer 120 may be formed by doping p-type impurities into any one of GaN, AlN, (AlGa) N, (InGa) N, (AlIn) N, or (AlGaIn) N. For example, the p-type impurity injected into the nitride semiconductor layer 120 may be magnesium (Mg).

As shown in FIGS. 4 and 8, the nitride semiconductor layer 120 may include a plurality of protrusions 125. For example, the protrusion 125 of the nitride semiconductor layer 120 may be formed in a pyramid or cone shape.

The nitride semiconductor layer 120 may be formed of a crystalline semiconductor and may reflect incident light.

The surface area of the nitride semiconductor layer 120 is extended by the plurality of protrusions 125, and the reflectance of incident light can be further increased.

The nitride semiconductor layer 120 may be formed of a crystalline semiconductor by metal-organic chemical vapor deposition (MOCVD). For example, the nitride semiconductor layer 120 may be formed to a thickness of 50 ~ 200nm.

Specifically, the nitride semiconductor layer 120 may be formed by injecting a source gas and a p-type impurity gas into a MOCVD chamber (not shown) maintained at a temperature of 500 to 1500 ° C.

The source gas may be a first source gas including any one of Tri-methyl Galium (TMGa), Tri-methyl Indium (TMIn), or Tri-methyl Aluminum (TMAl) and a second source gas including NH ₃ . . The p-type impurity gas may be Cp ₂ Mg (Biscyclopentadienyl magnesium). In addition, H ₂ and Ar gas may be used as the carrier gas.

First, referring to FIG. 2, the inside of the MOCVD chamber (not shown) is maintained at a low pressure first pressure. In addition, a first process of injecting the first source gas into the chamber and forming a plurality of liquid drops 121 on the back electrode 110 is performed.

For example, the first process may be performed by applying a pressure of 50 to 150 mtorr and supplying 1 to 3 Sccm of TMGa gas for 50 to 70 seconds.

By the first process, liquid drops 121 including gallium (Ga) may be grown on the back electrode 110.

Next, referring to FIG. 3, the inside of the chamber (not shown) is maintained at a second pressure higher than the first pressure. In addition, a second process of crystallizing the liquid drop 121 is performed by injecting the first source gas, the second source gas, and the p-type impurity gas.

In this case, an injection ratio of the first source gas, the second source gas, and the p-type impurity gas may be supplied as 1: 500 to 1000: 0.5.

For example, in the second process, a pressure of 150 to 250 mtorr is applied, and 1 to 3 Sccm of TMGa gas, 800 to 1500 Sccm of NH ₃ gas, and 1 to 2 Sccm of Mg gas are supplied for 500 to 600 seconds. You can proceed.

Nitrogen and p-type impurities may be doped into the liquid drops 121 by the second process, and a p-type gallium nitride (p-doped GaN) layer may be grown.

In particular, the liquid drops 121 may be crystallized by the second process, and may be formed as the protrusions 125 having a pyramid or cone shape.

Next, referring to FIG. 4, only a second source gas is injected into the chamber (not shown), and a third process of stabilizing crystal grains of the p-type gallium nitride film is performed by lowering the temperature to room temperature.

For example, the third process may be performed by lowering the chamber temperature to 1 to 30 ° C. and supplying an NH ₃ gas of 800 to 1500 Sccm.

Nitrogen ions may be released from the p-type gallium nitride layer after the first and second processes. In order to prevent this, a cooling process, which is the third process, may be performed to stabilize crystal grains of the p-type gallium nitride layer.

As described above, the nitride semiconductor layer 120 may be formed through the first to third processes by the MOCVD method.

The nitride semiconductor layer 120 formed by MOCVD has very good crystallinity and may have high conductivity. In addition, when the nitride semiconductor layer 120 is formed, damage to the rear electrode 110 formed at the bottom may be prevented.

The nitride semiconductor layer 120 includes p-type impurities. Thus, ohmic bonding and sheet resistance of the nitride semiconductor layer 120 may be improved.

Since the nitride semiconductor layer 120 includes a protrusion 125 formed by crystallization of the liquid drop 121, the surface area of the nitride semiconductor layer 120 may be expanded.

The nitride semiconductor layer 120 may increase the reflectance of the incident light and increase the light path.

Accordingly, the light absorption rate of the light absorption layer formed on the nitride semiconductor layer 120 can be improved.

Referring to FIG. 5, a light absorbing layer 130 is formed on the nitride semiconductor layer 120.

The light absorbing layer 130 includes an Ib-IIIb-VIb-based compound.

In more detail, the light absorbing layer 130 may include a copper-indium-gallium-selenide-based (Cu (In, Ga) Se ₂ , CIGS-based) compound or a copper-indium-selenide-based (CuInSe ₂ , CIS-based) compound. It may include.

For example, in order to form the light absorbing layer 130, a CIG-based metal precursor film is formed on the nitride semiconductor layer 120 using a copper target, an indium target, and a gallium target.

Subsequently, the metal precursor layer reacts with selenium (Se) by a selenization process to form a CIGS-based light absorbing layer 130.

In addition, the light absorbing layer 130 may form copper (Cu), indium (In), gallium (Ga), selenide (Se) by co-evaporation or MOCVD.

The light absorbing layer 130 receives external light and converts the light into electrical energy.

The light absorbing layer 130 generates photo electromotive force by the photoelectric effect.

For example, the light absorbing layer 130 may be formed to a thickness of 1000 ~ 1500nm. In addition, the carrier concentration of the light absorbing layer 130 may be 1 × 10 ¹⁴ to 1 × 10 ¹⁶ atom / cm 2.

That is, the light absorbing layer 130, which is a p-type semiconductor layer, is formed on the nitride semiconductor layer 120 doped with p-type impurities to obtain good interfacial characteristics.

The thickness of the light absorbing layer 130 can be reduced to 1/2 or less compared to the conventional. This is because the nitride semiconductor layer 120 serves as a reflective film.

That is, the light passing through the light absorbing layer 130 may be reflected by the nitride semiconductor layer 120 to proceed to the light absorbing layer 130 again. Accordingly, the propagation path of the incident light is doubled, thereby improving the light absorption rate of the light absorbing layer 130.

In particular, since pyramidal protrusions 125 are formed on the surface of the nitride semiconductor layer 120, the light path of incident light may be longer, and the light absorption may be further improved.

Since the thickness of the light absorbing layer 130 can be reduced, material cost reduction and productivity can be improved.

Referring to FIG. 6, a buffer layer 140 and a high resistance buffer layer 150 are formed on the light absorbing layer 130.

The buffer layer 140 may be formed of at least one or more layers on the light absorbing layer 130, and may be formed by stacking cadmium sulfide (CdS).

In this case, the buffer layer 140 is an n-type semiconductor layer, the light absorbing layer 130 is a p-type semiconductor layer. Accordingly, the light absorbing layer 130 and the buffer layer 140 form a pn junction.

The buffer layer 140 may be further formed with a zinc oxide layer on the cadmium sulfide (CdS) by performing a sputtering process targeting zinc oxide (ZnO).

The high resistance buffer layer 150 may be formed as a transparent electrode layer on the buffer layer 140.

For example, the high resistance buffer layer 150 may be formed of any one of ITO, ZnO, and i-ZnO.

The buffer layer 140 and the high resistance buffer layer 150 are disposed between the light absorbing layer 130 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 130 and the front electrode is large, the buffer layer 140 and the high resistance buffer layer 150 having a band gap in between the two materials are inserted into a good one. A junction can be formed.

Meanwhile, the buffer layer 140 and the high resistance buffer layer 150 may be formed by MOCVD.

In the exemplary embodiment, two buffer layers are formed on the light absorbing layer 130, but the present invention is not limited thereto, and the buffer layer may be formed of only one layer.

Referring to FIG. 7, the front electrode 160 is formed by stacking a transparent conductive material on the high resistance buffer layer 150.

The front electrode 160 may be formed of zinc oxide or indium tin oxide (ITO) including impurities such as aluminum (Al), alumina (Al ₂ O ₃ ), magnesium (Mg), and gallium (Ga). .

The front electrode 160 may be formed by MOCVD.

For example, the front electrode 160 may be formed of zinc oxide doped with aluminum or alumina by sputtering to form an electrode having a low resistance value.

That is, the front electrode 160 is a window layer forming a pn junction with the light absorbing layer 130. Since the front electrode 160 functions as a transparent electrode on the front of the solar cell, zinc oxide (ZnO) having high light transmittance and high electrical conductivity is provided. Is formed.

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 7 are sectional views showing the manufacturing process of the solar cell according to the embodiment.

8 is a perspective view of FIG. 7.

Claims (11)

Board; A back electrode formed on the substrate; A light absorbing layer formed on the back electrode; A front electrode formed on the light absorbing layer; And A nitride semiconductor layer formed between the back electrode and the light absorbing layer; Solar cell comprising a. The method of claim 1, The nitride semiconductor layer is a solar cell comprising a plurality of projections. The method of claim 1, The nitride semiconductor layer is any one of GaN, AlN, InN (AlGa) N, (InGa) N, (AlIn) N and (AlGaIn) N. The method of claim 1, The nitride semiconductor layer is formed of a nitride film doped with p-type impurities. The method of claim 1, The back electrode and the light absorbing layer is a solar cell having a ratio of the thickness of 1: 1 ~ 1.5. The method of claim 1, The light absorbing layer has a first impurity concentration, and the nitride semiconductor layer has a second impurity concentration higher than the first impurity concentration. Forming a back electrode on the substrate; Forming a nitride semiconductor layer on the back electrode; Forming a light absorbing layer on the nitride semiconductor layer; And Forming a front electrode on the light absorbing layer manufacturing method of a solar cell. The method of claim 7, wherein And the nitride semiconductor layer is formed of a nitride film doped with p-type impurities. The method of claim 7, wherein The nitride semiconductor layer is a manufacturing method of a solar cell comprising a plurality of projections. The method of claim 7, wherein The nitride semiconductor layer is formed by a MOCVD process using a first source gas including TMGa, TMIn, and TMAl and a second source gas including NH ₃ , Forming the nitride semiconductor layer, A first process of forming a liquid drop by applying a first pressure to the chamber into which the first source gas is injected; And And a second step of injecting the first, second source gas and p-type source gas into the chamber, and applying a second pressure higher than the first pressure to crystallize the liquid drop. The method of claim 10, After crystallizing the liquid drop by the second process, A third step of cooling the liquid crystallized by providing the second source gas inside the chamber and maintaining the temperature of the chamber at room temperature; A method of manufacturing a solar cell supplied with a third source gas containing a p-type impurity when the second process is performed.

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