EP2534704A1

EP2534704A1 - Solar cell and method for manufacturing the same

Info

Publication number: EP2534704A1
Application number: EP11856637A
Authority: EP
Inventors: Do Won Bae
Original assignee: LG Innotek Co Ltd
Current assignee: LG Innotek Co Ltd
Priority date: 2011-01-25
Filing date: 2011-10-06
Publication date: 2012-12-19
Also published as: KR101134730B1; CN102959735A; WO2012102454A1; JP2014503129A; CN102959735B

Abstract

Disclosed are a solar cell and a method for manufacturing the same. The solar cell includes a support substrate, a reflective layer on the support substrate, an oxidation layer formed on the reflective layer and including a material a same as a material of the reflective layer, a back electrode layer on the oxidation layer, a light absorbing layer on the back electrode layer, a buffer layer on the light absorbing layer, and a window layer on the buffer layer.

Description

SOLAR CELL AND METHOD FOR MANUFACTURING THE SAME

The embodiment relates to a solar cell and a method for manufacturing the same.

Recently, as energy consumption is increased, the development on a solar cell to convert solar energy into electrical energy has been performed.

In particular, a CIGS-based solar cell has been extensively used, in which the CIGS-based solar cell is a PN hetero junction device having a support substrate structure including a glass support substrate, a metallic back electrode layer, a P type CIGS-based light absorbing layer, a buffer layer, and an N type transparent electrode layer.

In addition, in order to increase the efficiency of the solar cell, various studies have been performed.

The embodiment provides a solar cell having photoelectric conversion efficiency and a method for manufacturing the same.

According to the embodiment, a solar cell includes a support substrate, a reflective layer on the support substrate, an oxidation layer formed on the reflective layer and including a material a same as a material of the reflective layer, a back electrode layer on the oxidation layer, a light absorbing layer on the back electrode layer, a buffer layer on the light absorbing layer, and a window layer on the buffer layer.

According to the embodiment, a method for manufacturing a solar cell includes forming a reflective layer on a support substrate including metal, forming an oxidation layer by oxidizing an upper portion of the reflective layer, forming a back electrode layer on the oxidation layer, forming a light absorbing layer on the back electrode layer, forming a buffer layer on the light absorbing layer, and forming a window layer on the buffer layer.

As described above, according to the embodiment, the reflective layer is formed on the support substrate, and the oxidation layer is formed by oxidizing the top surface of the reflective layer. Accordingly, the reliability and the photoelectric conversion efficiency of the solar cell can be improved.

FIG. 1 is a sectional view showing a solar cell according to the embodiment; and

FIGS. 2 to 5 are sectional views showing the method for manufacturing the solar cell according to the embodiment.

In the description of the embodiments, it will be understood that, when a layer (or film), a region, a pattern, or a structure is referred to as being onn or under another substrate, another layer (or film), another region, another pad, or another pattern, it can be directly or indirectly on the other substrate, layer (or film), region, pad, or pattern, or one or more intervening layers may also be present. Such a position of the layer has been described with reference to the drawings. The thickness and size of each layer shown in the drawings may be exaggerated, omitted or schematically drawn for the purpose of convenience or clarity. In addition, the size of elements does not utterly reflect an actual size.

FIG. 1 is a sectional view showing a solar cell according to the embodiment. Referring to FIG. 1, the solar cell according to the embodiment includes a support substrate 100, a reflective layer 200 on the support substrate 100, an oxidation layer 250 on the reflective layer 200, a back electrode layer 300 on the oxidation layer 250, a light absorbing layer 400 on the back electrode layer 300, a buffer layer 500 on the light absorbing layer 400, and a window layer 600 on the buffer layer 500.

The support substrate 100 has a plate shape to support the reflective layer 200, the oxidation layer 250, the back electrode layer 300, the light absorbing layer 400, the buffer layer 500, and the window layer 600.

The support substrate 100 may include an insulator. The support substrate 100 may be transparent. The support substrate 100 may be rigid or flexible.

The support substrate 100 may include metal. In more detail, the support substrate 100 may include a material selected from the group consisting of iron (Fe), nickel (Ni), and chrome (Cr). The support substrate 100 may be transparent, and rigid or flexible.

When the support substrate 100 includes metal, the support substrate 100 requires production cost less than that of a support substrate including glass, so that an advantageous economical effect can be obtained. In addition, the support substrate 100 is flexible, so that the support substrate 100 has an advantage in terms of portability.

However, when the support substrate 100 includes metal, metallic ions contained in the support substrate 100 may be diffused to the upper layer. Accordingly, the electrical characteristic of the solar cell may be degraded.

Therefore, the ions contained in the support substrate 100 can be prevented from being diffused upward by forming the oxidation layer 250. In other words, the oxidation layer 250 may serve as an anti-diffusion layer.

Since light incident onto the support substrate 100 through the light absorbing layer 400 may be reflected to the light absorbing layer 400 by the reflective layer 200, the photoelectric conversion efficiency can be improved.

The reflective layer 200 may include silicon oxide (SiO_x) or alumina (Al₂O₃). In addition, the reflective layer 200 may be used as a hetero junction layer.

If the hetero junction layer including Ti/SiO_xis used as the reflective layer 200, since a material such as SiOx is deposited after Ti has been deposited, the number of the processes is increased. Accordingly, the productivity must be improved.

According to the embodiment, after forming the reflective layer 200 on the support substrate 100, the reflective layer 200 is oxidized to form the oxidation layer 250. Accordingly, the convenience can be improved in the manufacturing process.

The reflective layer 200 may include a material constituting an oxidation film. For example, the reflective layer 200 may include a material selected from the group consisting of tantalum (Ta), tungsten (W), aluminum (Al), magnesium (Mg), neodymium (Nd), zirconia, beryllium (Be), and titan (Ti).

The reflective layer 200 reflects a light, which is incident to the support substrate 100 through the light absorbing layer 400, to the light absorbing layer 400, so that the photoelectric conversion efficiency of the solar cell can be improved.

If the reflective layer 200 has a thickness of about 10nm or less, the reflectance of a light passing through the light absorbing layer 400 may be reduced. If the reflective layer 200 has a thickness of about 5000nm or more, the reduction in the size of the device may be difficult. Accordingly, the reflective layer 200 may preferably have a thickness of about 10nm to abut 5000nm.

The thickness of the reflective layer 200 may be more reduced from an initial thickness through an oxidation treatment. In addition, the sum of the thicknesses of the reflective layer 200 and the oxidation layer 250 after the oxidation treatment has been performed may be greater than the thickness of the reflective layer 200 before the oxidation treatment is performed.

The oxidation layer 250 may lengthen the path of ions contained in the support substrate 100 at the high temperature, and can prevent the ions of the support substrate 100 from diffusing upward beyond the back electrode layer 300 because the oxidation layer 250 has ionic bonds and covalent bonds.

If the thickness of the oxidation layer 250 formed through the oxidation treatment becomes 5% or less of the initial thickness of the reflective layer 200, ions contained in the support substrate 100 are less prevented from being diffused upward beyond the back electrode layer 300. If the thickness of the oxidation layer 250 becomes at least 80% of the initial thickness of the reflective layer 200, the reflection effect of the reflection layer 200 may be reduced. Accordingly, the thickness of the oxidation layer 250 preferably becomes in the range of 5% to 80% of the initial thickness of the reflective layer 200.

The back electrode layer 300 may be formed on the oxidation layer 250. The back electrode layer 300 is a conductive layer. The back electrode layer 300 moves charges generated from the light absorbing layer 400 of the solar cell, so that current can flow to the outside of the solar cell. The back electrode layer 300 must represent high electrical conductivity and low resistivity in order to perform the above function.

The back electrode layer 300 must maintain stability in the high temperature condition when heat treatment is performed under sulfur (S) or selenium (Se) atmosphere as a CIGS compound is formed.

The back electrode layer 300 may include a material selected from the group consisting of Mo, Ni, Au, Al, Cr, W and Cu. In particular, the Mo overall satisfies the characteristics required for the back electrode layer 300.

The back electrode layer 300 may include at least two layers. In this case, the layers may include the same metal or different metals.

The light absorbing layer 400 may be formed on the back electrode layer 300. The light absorbing layer 400 includes a P type semiconductor compound. In detail, the light absorbing layer 400 includes group I-III-VI compounds. For example, the light absorbing layer 400 may have a Cu-In-Ga-Se-based crystal structure (Cu(In,Ga)Se₂;CIGS), a Cu-In-Se-based crystal structure, or a Cu-Ga-Se based crystal structure. The energy band gap of the light absorbing layer 400 may be in the range of about 1eV to about 1.8eV.

The buffer layer 500 may be formed on the light absorbing layer 400. According to the embodiment, the solar cell including a CIGS compound constituting the light absorbing layer 400 forms a PN junction between a CIGS compound, which constitutes a P type semiconductor, and a window layer 600 which constitutes an N type semiconductor. However, since two above materials represent great difference in a lattice constant and band gap energy, a buffer layer having intermediate band gap between the band gaps of the two materials is required in order to form a superior junction.

The buffer layer 500 includes CdS or ZnS, and the CdS represents more improved generating efficiency of the solar cell. A CdS thin film is an N type semiconductor, and may be doped with In, Ga, or Al to obtain a low resistance value.

The window layer 600 may be formed on the buffer layer 500. The window layer 600 is transparent and serves as a conductive layer. The window layer 600 includes an oxide material. For example, the window layer 600 may include zinc oxide, indium tin oxide (ITO) or indium zinc oxide (IZO).

In addition, the oxide material may include conductive impurities such as Al, Al₂O₃, Mg or Ga. In more detail, the window layer 600 may include Al doped zinc oxide (AZO) or Ga doped zinc oxide (GZO).

As described above, according to the embodiment, the photoelectric conversion efficiency can be improved.

In addition, ions contained in the support substrate 100 can be prevented from being diffused to the upper layer by the oxidation layer 250, so that the reliability for the solar cell can be improved.

In addition, the oxidation layer 250 is formed by performing the oxidation treatment with respect to the upper portion of the reflective layer 200. Accordingly, the convenience in the manufacturing process is increased, so that the productivity can be improved.

The details of the method for manufacturing the solar cell will be given based on the description about the solar cell. The description about the solar cell can be intrinsically matched with the description about the method for manufacturing the solar cell.

As shown in FIG. 2, the reflective layer 200 may be formed on the support substrate 100.

The reflective layer 200 may be formed through a sputtering scheme or a vacuum evaporation scheme.

Referring to FIG. 3, the oxidation layer 250 may be formed on the upper portion of the reflective layer 200. The oxidation layer 250 may be formed by performing an oxidation treatment with respect to the upper portion of the reflective layer 200. In other words, the oxidation layer 250 may include an oxide of the reflective layer 200.

The oxidation treatment may be performed through a PEO (plasma-electrolyte oxidization) scheme or an ED (electro deposition) scheme.

The thickness of the oxidation layer 250 formed through the oxidation treatment may be formed in the range of about 5% to about 80% of the thickness of the reflective layer 200.

In addition, the sum of the thicknesses of the reflective layer 200 and the oxidation layer 250 after the oxidation treatment has been performed may be greater than the thickness of the reflective layer 200 before the oxidation treatment is performed.

Referring to FIG. 4, the back electrode layer 300 may be formed on the oxidation layer 250. The back electrode layer 300 may be formed through a PVD (Physical Vapor Deposition) scheme or a plating scheme by using Mo.

Next, the light absorbing layer 400 may be formed on the back electrode layer 300. For example, the light absorbing layer 400 may be formed through various schemes such as a scheme of forming a Cu(In,Ga)Se2 (CIGS) based-light absorbing layer 400 by simultaneously evaporating Cu, In, Ga, and Se, or by separately evaporating Cu, In, Ga, and Se and a scheme of performing a selenization process after a metallic precursor film has been formed.

Regarding the details of the selenization process after the formation of the metallic precursor layer, the metallic precursor layer is formed on the back electrode layer 300 through a sputtering process employing a Cu target, an In target, or a Ga target.

Referring to FIG. 5, the buffer layer 500 may be formed on the light absorbing layer 400. The buffer layer 500 may be formed by depositing cadmium sulfide through a sputtering process or a CBD (chemical bath deposition) scheme.

Next, the window layer 600 may be formed on the buffer layer 500. The window layer 600 may be formed through a CVD process or a sputtering process.

As described above, according to the embodiment, the solar cell having improved photoelectric conversion efficiency improved by the reflective layer 200 can be provided.

In addition, ions contained in the support substrate 100 can be prevented from being diffused to the upper layer by the oxidation layer 250. Accordingly, the reliability of the solar cell can be improved.

Oxidation treatment is performed with respect to the upper portion of the oxidation layer 200, so that the convenience in the manufacturing process and the productivity can be improved.

Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effects such feature, structure, or characteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure.　 More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims.　 In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.

Claims

A solar cell comprising:

a support substrate;

a reflective layer on the support substrate;

an oxidation layer formed on the reflective layer and including a material a same as a material of the reflective layer;

a back electrode layer on the oxidation layer;

a light absorbing layer on the back electrode layer;

a buffer layer on the light absorbing layer; and

a window layer on the buffer layer.
The solar cell of claim 1, wherein the reflective layer includes at least one selected from the group consisting of tantalum (Ta), tungsten (W), aluminum (Al), magnesium (Mg), neodymium (Nd), zirconia, titan (Ti), and beryllium (Be).
The solar cell of claim 1, wherein the reflective layer has a thickness in a range of about 10nm to about 5000nm.
The solar cell of claim 3, wherein the oxidation layer has a thickness in a range of about 5% to about 80% based on the thickness of the reflective layer.
The solar cell of claim 1, wherein the support substrate includes at least one of iron (Fe), nickel (Ni), and chromium (Cr).
The solar cell of claim 1, wherein the back electrode layer includes a metallic material and is prepared as a multiple layers.
A method for manufacturing a solar cell, the method comprising:

forming a reflective layer on a support substrate including metal;

forming an oxidation layer by oxidizing an upper portion of the reflective layer;

forming a back electrode layer on the oxidation layer;

forming a light absorbing layer on the back electrode layer;

forming a buffer layer on the light absorbing layer; and

forming a window layer on the buffer layer.
The method of claim 7, wherein the oxidation layer is formed on the reflective layer through a PEO (plasma-electrolyte oxidization) scheme or an ED (electro deposition) scheme.
The method of claim 7, wherein the reflective layer includes at least one selected from the group consisting of tantalum (Ta), tungsten (W), aluminum (Al), magnesium (Mg), neodymium (Nd), zirconia, titan (Ti), and beryllium (Be).
The method of claim 7, wherein the oxidation layer has a thickness in a range of about 5% to about 80% based on a thickness of the reflective layer.