Method of manufacturing thin-film light-absorbing layer, and method of manufacturing thin-film solar cell using the same

Disclosed is a method of manufacturing a thin-film light-absorbing layer using spraying, including mixing precursor solutions comprising CuCl2, InCl3 and SeC(NH2)2 under a nitrogen atmosphere at room temperature thus preparing a mixture solution; spraying the mixture solution on a substrate and drying it, thus forming a thin film; and selenizing the thin film under a selenium atmosphere. A method of manufacturing a thin-film solar cell is also provided, which includes forming a back contact layer on a glass substrate using sputtering; forming a light-absorbing layer on the back contact layer using spraying; forming a buffer layer on the light-absorbing layer using chemical vapor deposition; forming a window layer on the buffer layer using sputtering; and forming an upper electrode layer on the window layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application Nos. 10-2010-0018121, filed Feb. 26, 2010 and 10-2010-0081632, filed Aug. 23, 2010, which are hereby incorporated by reference in their entirety into this application.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method of manufacturing a thin-film light-absorbing layer and a method of manufacturing a thin-film solar cell using the same.

2. Description of the Related Art

Materials for use in thin-film solar cells include crystalline silicon, amorphous silicon, a dye sensitizer, CIS, CIGS, CdTe, etc. Among these materials, a CIS-based compound which shows the highest theoretical efficiency is useful in the fabrication of solar cells. Currently, a CIS-based thin-film light-absorbing layer is being manufactured using a high-vacuum apparatus via co-evaporation or sputtering. As is known to date, the light conversion efficiency is about 15% at its maximum in the case of a CIS-based thin-film light-absorbing layer, and is about 20% in the case of a CIGS-based thin-film light-absorbing layer.

Although deposition of a CIS-based thin-film light-absorbing layer manufactured in a high vacuum may result in a solar cell having high efficiency, it is expensive to manufacture the light-absorbing layer, it is difficult to make one with a large area, and an expensive apparatus is needed to produce a large-area solar cell. Moreover, methods of manufacturing a light-absorbing layer from four elements such as CIGS using co-evaporation or sputtering in a vacuum are disadvantageous because an apparatus typically used therefor is high-priced, and also because the light-absorbing layer is manufactured by controlling the composition of four elements or individual binary compounds, and thus the composition is difficult to control and the manufacturing cost may increase.

Hence, research into methods of manufacturing high-efficiency thin-film solar cells not in a vacuum but in a non-vacuum where it is easier to control the composition and process, compared to CIGS-based compound solar cells typically manufactured using co-evaporation or sputtering, is ongoing. That is, in the case of thin-film solar cells manufactured using co-evaporation or sputtering in a vacuum, they have remarkably lower price competitiveness compared to fossil-fuel power cost.

Korean patent application publication No. 10-2009-0121660A discloses a method of manufacturing a CIGS thin film and a light-absorbing layer of a solar cell manufactured using the same, in which a copper precursor, an indium precursor, a gallium precursor, and a selenium precursor are mixed with water or a buffer thus preparing a mixture solution, after which voltage is applied to a potentiostat so that a CIGS thin film is electrodeposited on a working electrode. Also, a method of manufacturing a CIGS thin film in a non-vacuum is disclosed, and a CIGS thin film is manufactured using prepared particles by means of spraying thus fabricating a cell having an efficiency of 11.7% (Chris Eberspacher Chris Fredric, Karen Pauls, Jack Serra, “Thin-film CIS alloy PV materials fabricated using non-vacuum, particles-based techniques”, Thin Solid Films Vol 387, 18-22 (2001)). On the other hand, Korean patent application publication No. 10-2006-0036190A discloses a method of manufacturing an indium oxide sulfide buffer layer for a Cu(In, Ga)Se2or Cu(In, Ga)(S, Se)2thin-film solar cell using solution growth and a solar cell fabricated using the same, in which an indium oxyhydroxide sulfide thin film which is a new buffer material is formed to a thickness of tens of nm using an inexpensive solution growth process and a thin-film solar cell is fabricated using the same. The new buffer material used in the above patent may be grown using solution growth without post heat treatment to thus fabricate a solar cell. Also, a method of manufacturing a CIGS thin film using a CIGS solution precursor is disclosed, in which the CIGS thin film is formed from a solution precursor of CIGS using non-vacuum thin film deposition (David B. Mitzi, Min Yuan, Wei Liu, Andrew J. Kellock, S. Jay Chey, Vaughn Deline, Alex G. Schrott, “A High-Efficiency Solution-Deposited Thin-Film Photovoltaic Device” Adv. Mat., 2008, 9999, 1-6). As such, the solution precursor used may include a hydrazine solution and the CIGS thin film is formed using spin coating. In the case of a cell manufactured using a spin coated CIGS thin film, it may exhibit a light efficiency of about 12%. These methods are problematic because coating is not directly performed using the solution precursor in a non-vacuum or hydrazine which is highly toxic is used, undesirably causing environmental problems and reducing long-term stability.

Therefore, many attempts are being made to manufacture a CIS- or CIGS-based thin film in a non-vacuum in order to more easily and inexpensively fabricate a light-absorbing layer and a solar cell having a large area.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems encountered in the related art, and an object of the present invention is to provide a method of more simply and inexpensively manufacturing a thin-film light-absorbing layer using a low-temperature, low-cost and non-vacuum process, compared to conventional methods.

Another object of the present invention is to provide a method of manufacturing a thin-film solar cell using the method of manufacturing a thin-film light-absorbing layer.

In order to accomplish the above objects, the present invention provides a method of manufacturing a thin-film light-absorbing layer, comprising mixing precursor solutions comprising CuCl2, InCl3and SeC(NH2)2under a nitrogen atmosphere at room temperature, thus preparing a mixture solution; spraying the mixture solution on a substrate and drying the mixture solution, thus forming a thin film; and selenizing the thin film under a selenium atmosphere.

In addition, the present invention provides a thin-film light-absorbing layer, manufactured by mixing precursor solutions comprising CuCl2, InCl3and SeC(NH2)2under a nitrogen atmosphere at room temperature thus preparing a mixture solution, spraying the mixture solution on a substrate, drying the mixture solution, and then performing selenization under a selenium atmosphere.

In addition, the present invention provides a method of manufacturing a CIS-based thin-film solar cell, comprising forming a back contact layer on a glass substrate using sputtering; spraying on the back contact layer a mixture solution of CuCl2, InCl3and SeC(NH2)2precursor solutions mixed under conditions of a nitrogen atmosphere and room temperature, and performing selenization, thus forming a CIS-based light-absorbing layer; forming a buffer layer on the light-absorbing layer using chemical vapor deposition; forming a window layer on the buffer layer using sputtering; and forming an upper electrode layer on the window layer.

In addition, the present invention provides a method of manufacturing a CIGS-based thin-film solar cell, comprising forming a back contact layer on a glass substrate using sputtering; spraying on the back contact layer a mixture solution of CuCl2, InCl3, GaCl3and SeC(NH2)2precursor solutions mixed under conditions of a nitrogen atmosphere and room temperature, and performing selenization, thus forming a CIGS-based light-absorbing layer; forming a buffer layer on the light-absorbing layer using chemical vapor deposition; forming a window layer on the buffer layer using sputtering; and forming an upper electrode layer on the window layer.

In addition, the present invention provides a thin-film solar cell, comprising a substrate; a back contact layer formed on the substrate using sputtering; a light-absorbing layer formed on the back contact layer by mixing precursor solutions comprising CuCl2, InCl3and SeC(NH2)2under a nitrogen atmosphere at room temperature thus preparing a mixture solution, spraying the mixture solution on the substrate, drying the mixture solution, and performing selenization under a selenium atmosphere; a buffer layer deposited on the light-absorbing layer using chemical bath deposition; a window layer formed on the buffer layer using sputtering; and an upper electrode layer formed on the window layer using sputtering.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention pertains to a method of manufacturing a thin-film light-absorbing layer, including mixing CuCl2, InCl3and SeC(NH2)2precursor solutions under conditions of a nitrogen atmosphere and room temperature, thus preparing a mixture solution; spraying the mixture solution on a substrate and then drying it, thus forming a thin film; and selenizing the thin film under a selenium (Se) atmosphere.

Below, the steps of the method of manufacturing the thin-film light-absorbing layer according to the present invention are described in detail.

In the method of manufacturing the thin-film light-absorbing layer according to the present invention, preparing the mixture solution is performed by mixing CuCl2, InCl3and SeC(NH2)2precursor solutions under conditions of a nitrogen atmosphere and room temperature.

The mixture solution thus prepared is represented by CuXInYSeZ(X=0.5˜1.4, Y=0.5˜1.4, Z=1˜6) by adjusting the solution composition of the precursor solutions. That is, the molar ratio of Cu, In and Se in the mixture solution is CuXInYSeZ(X=0.5˜1.4, Y=0.5˜1.4, Z=1˜6). The precursor solution may further include GaCl3. As such, the mixture solution may contain Ga of GaCl3which replaces some percentage (20%) of In.

In the method of manufacturing the thin-film light-absorbing layer according to the present invention, forming the thin film is performed by spraying the mixture solution on the substrate and then drying it.

Herein, spraying may be carried out in a non-vacuum. Also, heating the substrate at 300˜500° C. for 30˜60 min is preferable, but a substrate thermally treated at 300˜500° C. for 30˜60 min before spraying may be used. The substrate is heated by means of a heater provided in the apparatus for manufacturing a thin-film light-absorbing layer. As such, the apparatus further includes an inlet port into which the mixture solution is introduced, a spray nozzle for spraying the mixture solution, a spray gun disposed between the inlet port and the spray nozzle so that the mixture solution is transferred by a carrier gas, and a rotary shaker provided under the heater. Upon spraying, the carrier gas is nitrogen and is preferably sprayed at 3˜50 ml/h, and the rotary shaker is rotated at 10˜50 rpm. The thin film deposited using spraying may be dried by being cooled to room temperature at a rate of 8˜12° C./min.

In the method of manufacturing the thin-film light-absorbing layer according to the present invention, selenizing is performed by allowing the thin film to stand at 450˜610° C. for 30˜120 min in a Se atmosphere.

In addition, the present invention pertains to a thin-film light-absorbing layer, manufactured by mixing CuCl2, InCl3and SeC(NH2)2precursor solutions under conditions of a nitrogen atmosphere and room temperature thus preparing a mixture solution, spraying the mixture solution on a substrate, drying it, and performing selenization in a Se atmosphere.

The mixture solution is composed of CuCl2, InCl3and SeC(NH2)2precursor solutions, and may further include a GaCl3precursor solution.

In addition, the present invention pertains to a method of manufacturing a CIS-based thin-film solar cell, including forming a back contact layer on a glass substrate using sputtering; spraying on the back contact layer a mixture solution of CuCl2, InCl3and SeC(NH2)2precursor solutions mixed under conditions of a nitrogen atmosphere and room temperature, and performing selenization, thus forming a CIS-based light-absorbing layer; forming a buffer layer on the light-absorbing layer using chemical vapor deposition; forming a window layer on the buffer layer using sputtering; and forming an upper electrode layer on the window layer.

Specifically, spraying is performed using an apparatus for manufacturing a thin-film light-absorbing layer comprising an inlet port into which the mixture solution is introduced, a spray nozzle for spraying the mixture solution, a spray gun disposed between the inlet port and the spray nozzle so that the mixture solution is transferred by a carrier gas, a heater for heating the substrate, and a rotary shaker provided under the heater.

In addition, the present invention pertains to a thin-film solar cell comprising a substrate210; a back contact layer220formed on the substrate210using sputtering; a light-absorbing layer230formed on the back contact layer220by mixing CuCl2, InCl3and SeC(NH2)2precursor solutions under conditions of a nitrogen atmosphere and room temperature thus preparing a mixture solution, spraying the mixture solution on the substrate, drying it, and performing selenization in a Se atmosphere; a buffer layer240deposited on the light-absorbing layer230using chemical bath deposition; a window layer250formed on the buffer layer240using sputtering; and an upper electrode layer270formed on the window layer250using sputtering.

The above purposes, features and advantages will become more apparent by means of the following description with reference to the appended drawings. In the description of the present invention, descriptions of known techniques are regarded as unnecessary and may be omitted when they would make the characteristics of the invention unclear.

Also, saying that any part “includes” any element means that another element is not excluded but is further included unless otherwise stated.

FIG. 1is a schematic view showing the apparatus for manufacturing a thin-film light-absorbing layer according to the present invention.

The apparatus100for manufacturing a thin-film light-absorbing layer as shown inFIG. 1includes the inlet port110into which the mixture solution111is introduced, the spray nozzle130for spraying the mixture solution111, the spray gun120disposed between the inlet port110and the spray nozzle130so that the mixture solution111is transferred by the carrier gas112, the heater140spaced apart from the spray nozzle130and provided at the lower portion of the apparatus so that the substrate210is heated, and the rotary shaker150provided under the heater140, and is used to spray the mixture solution in a non-vacuum.

The mixture solution111is obtained by mixing CuCl2, InCl3and SeC(NH2)2precursor solutions in a nitrogen atmosphere so that as little contaminant as possible is added, and mixing is preferably carried out at room temperature for about 5 min so that the reaction of precursor solutions efficiently takes place. As such, the solution composition of precursor solutions is appropriately adjusted thus preparing the mixture solution111represented by CuXInYSeZ(X=0.5˜1.4, Y=0.5˜1.4, Z=1˜6). Also, the precursor solutions further includes GaCl3and thus the mixture solution may contain Ga of Gacl3which replaces some percentage (20%) of In.

The method of manufacturing the thin-film light-absorbing layer using the apparatus100for manufacturing a thin-film light-absorbing layer is specifically described herein. The molybdenum (Mo) back contact layer220deposited on the glass substrate210is maintained at 300˜500° C. using the heater140, after which nitrogen gas serving as the carrier gas112is controlled so as to be uniformly sprayed at 3˜50 ml/h in order to prevent the mixture solution111from becoming contaminated, and the substrate210having the Mo back contact layer220is rotated at 10˜50 rpm by means of the rotary shaker150so that the mixture solution111is uniformly sprayed on the Mo back contact layer220. As such, the substrate210having the Mo back contact layer220may be heated at 300˜500° C. for 30˜60 min, or may be heated before spraying. This heating process plays a role in enhancing the adhesion of the Mo back contact layer220to the glass substrate210, and thus problems in which the Mo thin film is separated during a subsequent process such as spraying do not occur. The thin-film light-absorbing layer deposited using spraying may be dried by being slowly cooled to room temperature at a rate of 8˜12° C./min.

In order to make the thin-film light-absorbing layer be dense and crystalline, selenization is preferably performed at 450˜610° C. for 30˜120 min. As such, the Se vapor used includes Se particles thus forming a selenization atmosphere.

The above is a description of the method of manufacturing the thin-film light-absorbing layer using spraying. Below, a CIS-based solar cell and a CIGS-based thin-film solar cell including the thin-film light-absorbing layer thus manufactured are described.

FIG. 2schematically shows the thin-film solar cell according to the present invention.

With reference toFIG. 2, the thin-film solar cell according to the present invention includes the back contact layer220, the CIS- or CIGS-based light-absorbing layer230, the buffer layer240, the window layer250, and the upper electrode layer270, which are sequentially formed on the substrate210.

The substrate210is a glass substrate, preferably a sodalime glass substrate. In addition thereto, a substrate made of the same or similar material may be used.

The back contact layer220is formed on the substrate210, and the material of the back contact layer is not particularly limited but typically includes Mo. The back contact layer is formed at a thickness of about 1 μm on the substrate using sputtering.

The CIS- or CIGS-based light-absorbing layer230is formed on the back contact layer220. The CIS- or CIGS-based light-absorbing layer is specified with reference toFIG. 1, and its specific description is omitted.

The buffer layer240is formed on the light-absorbing layer230by depositing cadmium sulfide (CdS) typically useful as a material of a light-absorbing layer using chemical bath deposition.

The window layer250functioning as a transparent electrode is formed on the buffer layer240by sequentially depositing i-ZnO and n-ZnO using sputtering. An optional antireflective layer260may be further formed on the window layer250.

The upper electrode layer270is formed on the window layer250by depositing aluminum (Al) to a thickness of about 1 μm using sputtering.

FIG. 3is a flowchart showing the process of manufacturing the thin-film solar cell according to the present invention.

With reference toFIG. 3, the CIS- or CIGS-based thin-film solar cell may be manufactured by forming the back contact layer on the substrate using sputtering (S300), heating the back contact layer (S310), mixing CuCl2, InCl3and SeC(NH2)2or CuCl2, InCl3, GaCl3and SeC(NH2)2precursor solutions under conditions of a nitrogen atmosphere and room temperature thus preparing the mixture solution (S320), spraying the mixture solution on the back contact layer (S330), drying it, performing selenization (S340), thus forming a CIS- or CIGS-based light-absorbing layer, forming the buffer layer on the light-absorbing layer using chemical bath deposition (S350), forming the window layer on the buffer layer using sputtering (S360and S370), and forming the upper electrode layer on the window layer using sputtering (S380).

Preparation of Mixture Solution

CuCl2, InCl3and SeC(NH2)2precursor solutions were blended in a nitrogen atmosphere so that as little contaminant as possible was added and then mixed at room temperature for about 5 min so that the reaction of respective reactants efficiently occurred, thus preparing a mixture solution represented by CuXInYSeZ(X=0.5˜1.4, Y=0.5˜1.4, Z=1˜6).

Formation of Thin Film

Nitrogen gas was controlled so as to be uniformly sprayed at 3˜50 ml/h on a Mo back contact layer heated at 300˜500° C. for 30˜60 min, and the substrate located under the Mo back contact layer was rotated at 10˜50 rpm, whereby the mixture solution was sprayed thereon, and the thin film thus formed was dried by being slowly cooled to room temperature at a rate of 8˜12° C./min, thus manufacturing a thin film 1 μm thick.

The thin film was selenized in a Se atmosphere at 450˜610° C. for 30˜120 min, thus manufacturing a CIS-based thin-film light-absorbing layer.

A thin-film light-absorbing layer was manufactured in the same manner as in Example 1, with the exception that GaCl3was further added to the mixture solution so that the mixture solution contained Ga which replaces some percentage (20%) of In.

Fabrication of CIS-Based Thin-Film Solar Cell

Formation of Back Contact Layer

Mo was deposited to a thickness of 1 μm on a glass substrate or a sodalime glass substrate using sputtering, thus forming a Mo back contact layer.

Formation of CIS-Based Light-Absorbing Layer

The CIS-based thin-film light-absorbing layer was formed to a thickness of 1 μm using the procedures of Example 1.

Formation of Buffer Layer

A CdS buffer layer was formed on the light-absorbing layer using chemical vapor deposition.

Formation of Window Layer

On the buffer layer, i-ZnO and n-ZnO were sequentially deposited using sputtering, thus forming a window layer.

Formation of Upper Electrode Layer

An Al upper electrode layer was formed to a thickness of 1 μm on the window layer using sputtering, thereby manufacturing a CIS-based thin-film solar cell.

Fabrication of CIGS-Based Thin-Film Solar Cell

A CIGS-based thin-film solar cell was manufactured in the same manner as in Example 3, with the exception that the CIGS-based thin-film light-absorbing layer was formed using the procedures of Example 2.

Test Example 1

Analysis of Surface of Thin-Film Light-Absorbing Layer

The surface of the thin film manufactured by the process of manufacturing a thin-film light-absorbing layer according to the present invention was analyzed using an SEM. The results are shown inFIGS. 4 and 5.

With reference toFIG. 4, the thin film manufactured using spraying in a non-vacuum is uniformly deposited to a predetermined thickness, and exhibits p-type semiconductor properties depending on the solution composition.

With reference toFIG. 5, the thin film of Example 1 is densely crystallized thanks to selenization under conditions of a Se atmosphere, 450˜610° C. and 30˜120 min.

Test Example 2

Analysis of Transmittance of Thin-Film Light-Absorbing Layer

The transmittance of the CIS-based thin-film light-absorbing layer manufactured using the method according to the present invention was measured. The results are shown inFIG. 6.

With reference toFIG. 6, the energy gap of the thin film of Example 1 is about 1.01 eV, which is almost the same as a theoretical value. The energy gap may be changed by adjusting the ratio of X, Y and Z of CuXInYSeZin the mixture solution precursor. Furthermore, the transmittance at a wavelength ranging from 400 nm to about 1000 nm is obtained because the thin film is slightly thin. When the thin film is deposited to a thickness of 1 μm or more, it can completely absorb light and is thus very efficient.

Test Example 3

Analysis of Solar Light Conversion Efficiency of CIS-Based Thin-Film Solar Cell

The solar light conversion efficiency of the CIS-based thin-film solar cell according to the present invention was measured. The results are shown inFIG. 7.

With reference toFIG. 7, the CIS-based thin-film solar cell of Example 3 exhibits the solar light conversion efficiency equal to that of a thin-film solar cell including a light-absorbing layer resulting from a solution process.

As described above, the present invention provides a method of manufacturing a thin-film light-absorbing layer and a method of manufacturing a thin-film solar cell. According to the present invention, a CIS- or CIGS-based light-absorbing layer can be manufactured using a low-temperature, low-cost and non-vacuum process, thus making it possible to more simply and inexpensively manufacture it, compared to conventional methods. A large area light-absorbing layer can be manufactured on a large scale.

Also, according to the present invention, an organic solvent such as an amine which undesirably causes environmental contamination is not used, thus reducing harm to the environment. Compared to a light-absorbing layer manufactured in a high vacuum, the light-absorbing layer according to the present invention enables a solar cell that has been used to easily be collected and disposed of, and thus can be usefully applied to fabricate a thin-film solar cell.