KR20110038391A - Method for fabricating chalcogenide solar cell - Google Patents

Abstract

PURPOSE: A method for manufacturing a chalcogenide solar cell is provided to improve photoelectric conversion efficiency by including hydrated sodium thin film. CONSTITUTION: A depositing solution including sodium compounds and solvent is prepared. A p type electrode and an opposite electrode are immersed in the depositing solution. A sodium hydrate thin film is formed on the upper side of the p type electrode by applying an electric field between the p type electrode and the opposite electrode. A chalcogenide solar cell is formed on the upper side of the sodium hydrate of the p type electrode. An N side electrode is formed on the upper side of the chalcogenide solar cell.

Description

Method for manufacturing chalcogenide-based solar cell {Method for fabricating chalcogenide solar cell}

The technology disclosed herein relates to a method for manufacturing a chalcogenide-based solar cell and a solar cell manufactured by the present invention, and more particularly, to manufacturing a chalcogenide-based solar cell having an improved photoelectric conversion efficiency by including a sodium hydrate thin film. It relates to a method and a solar cell produced thereby.

There is a need for clean and unlimited energy that is different from the existing energy, such as a sense of crisis of exhaustion of oil resources, the entry into force of the Kyoto Protocol's climate change agreement, and the explosive demand for energy due to the economic growth of emerging BRICs. This is going on. Among the renewable energy, solar cells (Solar Cells or Photovoltaic Cells) are the core elements of photovoltaic power generation that converts sunlight directly into electricity, and are widely used for power supply from space to home. In the early days when solar cells were first made, they were mainly used for space use, but after two oil surges in the 1970s, they were attracting attention for their potential as ground power sources. It has been started for use. Recently, it has been used in aviation, meteorology, and communication fields, and solar vehicles and solar air conditioners are also attracting attention.

Such solar cells mainly use silicon or compound semiconductors, but because they are manufactured in the semiconductor device manufacturing process, the manufacturing cost is high, and silicon solar cells, which occupy the main part of the solar cells, have difficulty in supplying silicon raw materials. . Under these circumstances, chalcogenide-based solar cells such as CIGS and CdTe, which do not use any silicon materials, have recently attracted much attention. Chalcogenide refers to a compound containing S, Se, Te, which is a chalcogen element, and the chalcogenide compound, which is widely applied in the field of solar cells, is composed of IB-IIIA-VIA group elements, CuInS ₂ (CIS), CuGaS ₂ (CGS), CuInSe ₂ (CISe), CuGaSe ₂ (CGSe), CuAlSe ₂ (CASe), CuInTe ₂ (CITe), CuGaTe ₂ (CGTe), Cu (In, Ga) S ₂ (CIGS ), Cu (In, Ga) Se ₂ (CIGSe), Cu ₂ ZnSnS ₄ (CZTS), and the like. The chalcogenide-based compound or thin film has a band gap energy of 1 to 2 eV, which has the best light absorption coefficient (1 x 10 ⁵ cm ^-1 ) among semiconductors and is very optically stable, so that the light absorption layer of the solar cell It is a very ideal material. Another chalcogenide compound used in the solar cell industry is CdS, which is composed of IIB-VIA group elements, and is suitable as a buffer material located at an interface where a PN junction is formed. Representative chalcogenide solar cells use CIGSe as a light absorption layer and CdS as a buffer layer. Various physicochemical manufacturing methods are used as the thin film formation method.

Generally, soda-lime glass is used to manufacture CIGSe thin film solar cells. The reason is that the thin film peeling phenomenon due to the difference in thermal expansion coefficient can be prevented because the thermal expansion coefficient of CIGSe and the linear thermal expansion coefficient of soda lime glass are the same. And sodium (Na) component contained in soda lime glass plays an important role to improve the film quality by diffusing into the CIGSe thin film. The effect of Na on the CIGSe-based absorption layer is as follows. As the particle diameter increases, the area of the Cu / (In + Ga) ratio which increases the (1 1 2) orientation, increases the hole concentration of the light absorption layer, improves uniformity on the large area substrate, and obtains high efficiency. Thus, attempts for the addition of Na components and uniform control have continued in recent years, and methods of adding materials such as NaF, Na ₂ Se, and Na ₂ S through vacuum deposition are mainly used.

If a flexible metal foil such as stainless steel is used as the substrate, the substrate itself does not contain Na. When using a substrate material containing no Na in this manner, it is essential to artificially add some Na compounds. In addition, in the case of soda-lime glass also contains an additional Na introduction process because there is a problem of insufficient Na content or inconsistency for each part.

In the conventional CIGSe-based thin film solar cell manufacturing process, the addition method of Na component is a method of doping the Na compound components such as NaF, Na ₂ Se, Na ₂ S, Na ₂ O ₂ using a vacuum process and after forming the CIGSe thin film There are methods for adding these materials, but these methods are difficult to control the composition of the Na component, and there are disadvantages of vacuum and high temperature conditions, and thus, an advanced improvement method for Na addition is required.

According to one embodiment, preparing an electrodeposition liquid containing a sodium compound and a solvent, immersing the P-side electrode and the counter electrode in the electrodeposition liquid, by applying an electric field between the P-side electrode and the counter electrode Forming a sodium hydrate thin film on the P-side electrode, forming a chalcogenide-based solar cell on the sodium hydrate thin film formed on the P-side electrode, and an N side on the chalcogenide-based solar cell Provided is a method for manufacturing a chalcogenide-based solar cell comprising forming an electrode.

According to another embodiment, a chalcogenide-based solar cell manufactured by the manufacturing method is provided.

Hereinafter, exemplary embodiments disclosed herein will be described in detail with reference to the accompanying drawings. The illustrative embodiments described above in the detailed description, drawings, and claims are not meant to be limiting, other embodiments may be utilized, and other changes may be made without departing from the spirit or scope of the subject matter disclosed herein. It is also possible. The components of the present disclosure, that is, those described generally herein and described in the figures, may be arranged, substituted, combined, and designed in a variety of different configurations, all of which are expressly contemplated, and It will be readily understood that they form part of the disclosure.

When one component or one layer is referred to as "on top of" or "on" another component or another layer, when the one component or one layer is formed directly on top of the other component or another layer Of course, it may also include the case where one or more components or layers are interposed therebetween.

The present disclosure provides a method for introducing a Na component that plays an important role in improving the film quality of the chalcogenide-based compound thin film in the manufacture of chalcogenide-based solar cells in order to solve the problems of the conventional source technology as described above.

According to one embodiment, the method for manufacturing a chalcogenide-based solar cell may be performed in the following order.

a) Prepare an electrodeposition liquid containing a sodium compound and a solvent. Next, the P-side electrode and the counter electrode are immersed in the electrodeposition liquid. b) an electric field is applied between the P-side electrode and the counter electrode to form a sodium hydrate thin film on the P-side electrode. c) forming a chalcogenide-based solar cell on the sodium hydrate thin film formed on the P-side electrode. d) A chalcogenide-based solar cell may be manufactured by forming an N-side electrode on the chalcogenide-based solar cell.

More specifically, chalcogenide-based solar cells may be manufactured in the following manner.

<Substrate / Metal Electrode>

As the substrate, soda lime silica glass or amorphous glass, metal foil, metal tape, flexible plastic such as polyimide, or the like can be used. The substrate may be subjected to a cleaning process immediately before use, for example, soaked in acetone, alcohol, water or a mixed solution thereof and then subjected to ultrasonic cleaning.

The P-side electrode of the solar cell may be manufactured by forming a metal electrode on the substrate. As the material of the metal electrode, any material having electrical conductivity can be used, but high electrical conductivity and ohmic bonding between the chalcogenide-based compound are possible, and tungsten (W), copper (Cu), Molybdenum (Mo), gold (Au), nickel (Ni) and the like are preferable. The thickness of the metal electrode is preferably about 0.1 to 5 μm. The metal electrode may be formed by DC sputtering, thermal evaporation or otherwise by chemical vapor deposition (CVD), atomic layer deposition (ALD), electroplating, or the like.

Sodium Hydrate Coating

First, a sodium compound is dissolved in a solvent or a dispersion medium to prepare an electrodeposition liquid. In order to improve the stability of the electrodeposition solution may additionally include additives such as water (H ₂ O), buffer solution, glycerin. The substrate on which the metal electrode is formed, that is, the P-side electrode is a working electrode, is immersed in the electrodeposition liquid together with a counter electrode, and then coated with sodium hydrate by electrodeposition.

1 is a view illustrating a process of coating sodium hydrate on the P-side electrode surface by electrodeposition. Referring to FIG. 1, a substrate on which a metal electrode is formed, that is, a working electrode (P-side electrode) is connected to a negative electrode (−), a counter electrode is connected to a positive electrode (+), and a DC electric field is applied in a range of 0.1 V to 200 V. Sodium hydrate can be coated on the P-side electrode surface. The counter electrode may be any material that exhibits conductivity, and stainless steel, copper plate, platinum, or the like may be used.

The sodium compound for preparing the electrodeposition liquid is not particularly limited as long as it contains sodium, and NaF, Na ₂ Se, Na ₂ S, Na (CH ₃ COO), Na ₂ CO ₃ , NaOH, NaCl, NaNO _3, and the like. May be used alone or in combination. As a solvent for dissolving the sodium compound, water, alcohols, organic solvents, and the like can be used, but these mixed liquids may be used. In particular, when the solvent is water, the electrodeposited sodium hydrate may be redissolved again in water, so it is preferable to use the mixture with a second solvent. The concentration of the electrodeposition liquid is preferably 0.1mM ~ 3M. At this concentration sodium hydrate may be uniformly coated. When sodium acetate is used as the sodium compound, the electrochemical reactions occurring at the cathode and anode are as follows.

The reaction at the ^{_{anode: 2H 2 O → 4H + +}} O 2 (g) + 4e -

_{^{CH 3 COO - + H + CH}} 3 COOH

The reaction at the ^{_{cathode: 2H 2 O + 2e - →}} 2OH - + H 2 (g)

Na ^{+ +} OH ^- → NaOH

As described above, sodium hydrate (NaOH) is formed on the surface of the metal electrode, which is the cathode, and serves as a Na source for the chalcogenide-based light absorbing layer.

<Calcozinide Solar Cell>

A chalcogenide-based solar cell is formed on the metal electrode on which the sodium hydrate thin film is formed to be in contact with the sodium hydrate thin film. The chalcogenide-based solar cell may have a structure in which a chalcogenide-based compound thin film that is a P-type semiconductor layer and a ZnO thin film that is an N-type semiconductor layer are bonded to each other. In addition, although a buffer layer such as CdS may be interposed between the P-type semiconductor layer and the N-type semiconductor layer, it is not necessary.

As the chalcogenide-based compound, CuInS ₂ (CIS), CuGaS ₂ (CGS), CuInSe ₂ (CISe), CuGaSe ₂ (CGSe), CuAlSe ₂ (CASe), CuInTe ₂ (CITe), CuGaTe ₂ (CGTe), Cu (In, Ga) S ₂ (CIGS), Cu (In, Ga) Se ₂ (CIGSe), Cu ₂ ZnSnS ₄ (CZTS), and the like, and the like, and examples thereof may be used alone or in combination of a plurality thereof. . The most representative CIGSe thin film may be deposited using a co-evaporation method using four metal elements (Cu, In, Ga, Se) as starting elements, and sputtering and selenization of these metal elements or compounds. The thin film may be formed. In addition, a thin film may be formed by using a wet method such as a printing process after preparing chalcogenide compounds or precursor nanoparticles without using a vacuum device as described above. It is good to form the thickness of such a P-type semiconductor layer about 1-3 micrometers. The chalcogenide-based compound is formed by the above method, and in this process, sodium formed on the surface of the metal electrode by the electrodeposition method is transferred to the chalcogenide-based compound layer, thereby improving the performance of the final absorbing layer.

I-ZnO (intrinsic ZnO) may be mainly used as the N-type semiconductor layer, and a thin film may be formed by a sputtering method, or a thin film may be formed by a wet method such as a printing process using ZnO nanoparticles. A thickness of ˜500 nm is suitable.

Since the energy gap between the CIGSe thin film, which is a P-type semiconductor layer, and the ZnO thin film, which is an N-type semiconductor layer is large, and a lattice constant difference is large, a buffer layer may be formed therebetween. This can help improve efficiency. Cadmium sulfide (CdS) may be used as the buffer layer material, but ZnS, Zn (O, S), ZnSe, (Zn, In) Se, In (OH, S), In _{2 that} do not use heavy metal Cd S ₂ and the like can be used. As a method for forming the buffer layer, a chemical bath deposition method, an ion layer gas reaction method, or a vacuum deposition method may be used, and a thickness of 10 to 500 nm may be appropriate. This buffer layer helps in efficiency but is not necessary for the operation of the solar cell.

<N side electrode>

An N-side electrode is formed on the i-ZnO thin film, which is an N-type semiconductor layer. Zn-based oxides, Sn-based oxides, In-based oxides, Ti-based oxides, metal nanoparticles, and the like may be used as the material for the N-side electrode, and an electrode thickness of about 5 to 400 nm is suitable. In more detail, doped ZnO (ZnO: Al, ZnO: B, ZnO: Ga, ZnO: N, etc.) based materials, SnO ₂ material, ITO material, TiO ₂ material, TiOx (1 <x <2) material using Thin film can be formed on top of chalcogenide-based solar cells by vacuum deposition (sputtering, thermal deposition, CVD, etc.), ZnO-based nanoparticles, doped ZnO-based nanoparticles, SnO ₂ nanoparticles, ITO nanoparticles. , TiO ₂ nanoparticles, TiOx (1 <x <2) nanoparticles, sol, metal nanoparticles and the like can also be formed by a wet method such as the printing process. In addition, the N-side electrode may be selected alone or a plurality of materials, such as doped ZnO, SnO ₂ , ITO, TiO ₂ , TiOx (1 <x <2), metal nanoparticles, etc., the structure is a single layer structure It may also be a laminated structure, such as two-layer structure and three-layer structure.

In the chalcogenide-based solar cell implemented by the manufacturing process as described above, a grid electrode and an antireflection layer may be further formed on the N-side electrode. The grid electrode is mainly composed of a metal contact layer and can be formed through an electron beam system or another method, and mainly Ni, Al, Ag, or the like can be used. MgF ₂ is generally used as the anti-reflection layer that reduces the reflection loss of sunlight incident to the solar cell and further increases the efficiency. The anti-reflection layer may be formed to have a thickness of 600 to 1000 Å by the electron beam evaporation method.

In the preparation of chalcogenide-based solar cells, the electrodeposition method adopted as a method for adding Na component to the absorber layer can be carried out under various process conditions. For example, it is possible to control the adhesion amount of Na adhered to the substrate by selecting the Na compound for electrodeposition, electrodeposition time, voltage control, change in Na concentration of the electrolyte solution, selection of the buffer solution, and the like. It is also possible to add Na with a uniform composition by adding the ionized Na component to the substrate surface using an electrochemical method. In particular, in the manufacturing of a CIGS-based solar cell to which a metal plate and a polymer-type flexible substrate are applied, the Na addition process for improving the absorption layer film quality can be effectively performed. In addition, the process can be carried out at room temperature and atmospheric pressure conditions, it is possible to apply a large area substrate at a relatively low process cost is very desirable as a commercial process for Na addition.

Hereinafter, the disclosed technology will be further embodied by examples, but the present invention is only presented for better understanding and the spirit of the disclosed technology is not limited to the following examples.

Example 1

To prepare the electrodeposition solution, 200 g of isopropyl alcohol was added to a glass beaker, followed by dissolving 50 mg of sodium acetate. To this solution, 0.5 g of a buffer solution and glycerin as a flocculation agent were added, followed by stirring for 30 minutes to prepare an electrodeposition solution. Molybdenum-coated stainless steel (hereinafter referred to as Mo electrode) and a cathode (relative electrode) copper plate were disposed to face each other at 3 cm intervals as a cathode. Electrodeposited at 10 V DC for 10 seconds to form a sodium hydrate thin film on the Mo electrode. CIGSe was formed on the sodium hydrate on the Mo electrode by co-evaporation (2 μm), and the CdS thin film, which is a buffer layer, was formed to a thickness of 50 nm using CBD (chemical bath deposition). An i-ZnO film was formed. ZnO: Al was formed on the N-type semiconductor as the N-side electrode. Pure ZnO, an N-type semiconductor, was deposited by RF magnetron sputtering. In the case of n-type ZnO (ZnO: Al), a target containing 2.5 wt% of Al was used. The Al grid electrode was formed using the electron beam to complete the solar cell device. The solar cell conversion characteristics were measured after calibration with a reference cell under AM 1.5, 100 100 / ㎠ conditions. 2 is a graph showing current-voltage characteristics of a solar cell having a sodium hydrate thin film formed by electrodeposition. Referring to FIG. 2, V _OC was 0.79 V, J _SC was 26.34 mA / cm ^2, and Fill Factor was 0.72, and the photoelectric conversion efficiency was 15.51%.

Comparative example

A solar cell was manufactured in the same manner as in Example 1, except that the forming process of the sodium hydrate thin film was omitted. The photoelectric conversion efficiency measurement result was 10.23%.

Example 2

After 150 g of butyl alcohol and 1 g of distilled water were added, 100 mg of NaNO ₃ was added to prepare an electrodeposition liquid. The electrodeposition liquid was used, and the other process was carried out similarly to Example 1, and manufactured the solar cell. The photoelectric conversion efficiency measured was 14.76%.

Example  3

After 200 g of ethyl alcohol and 2 g of distilled water were added, 50 mg of sodium nitrate was added to prepare an electrodeposition liquid. The electrodeposition liquid was used, and the other process was carried out similarly to Example 1, and manufactured the solar cell. The photoelectric conversion efficiency measurement result was 13.89%.

Example 4

In the solar cell manufacturing process shown in Example 1, the absorption layer was used as CIGS instead of CIGSe, the buffer layer was used as ZnS instead of CdS, and the same as in Example 1 except that ITO was used instead of ZnO: Al. To prepare a solar cell. The photoelectric conversion efficiency measurement result was 13.39%.

Example 5

A solar cell was manufactured in the same manner as in Example 1, except that W was used instead of the Mo electrode in the solar cell manufacturing process shown in Example 1. The photoelectric conversion efficiency measured was 12.17%.

As described above, by using the electrodeposition method in thin film solar cell manufacturing, precise Na component control is possible, and high quality thin film manufacturing can be realized. In particular, in the production of a CIGS-based solar cell to which a metal plate and a polymer-type flexible substrate not containing Na component are applied, an Na addition process for improving the absorption layer film quality may be effectively performed. The technology disclosed in the present specification is not only capable of processing at room temperature and atmospheric pressure conditions, but also can be applied to large-area substrates at relatively low process costs, thereby increasing economic efficiency and increasing solar cell efficiency, thereby creating economic value effects such as reducing production costs. Big.

1 is a view illustrating a process of coating sodium hydrate on the P-side electrode surface by electrodeposition.

2 is a graph showing current-voltage characteristics of a solar cell having a sodium hydrate thin film formed by electrodeposition.

Claims (9)

Preparing an electrodeposition liquid containing a sodium compound and a solvent; Dipping the P-side electrode and the counter electrode in the electrodeposition liquid; Applying an electric field between the P-side electrode and the counter electrode to form a sodium hydrate thin film on the P-side electrode; Forming a chalcogenide-based solar cell on the sodium hydrate thin film formed on the P-side electrode; And Method of manufacturing a chalcogenide-based solar cell comprising the step of forming an N-side electrode on the chalcogenide-based solar cell. The chalcogenide of claim 1, wherein the sodium compound is at least one selected from the group consisting of NaF, Na ₂ Se, Na ₂ S, Na (CH ₃ COO), Na ₂ CO ₃ , NaOH, NaCl, and NaNO ₃ . Method for producing a solar cell. The method of claim 1, wherein the electrodeposition solution further comprises at least one additive selected from the group consisting of water (H ₂ O), a buffer solution and glycerin. The method of claim 1, wherein the concentration of the electrodeposition liquid is 0.1mM to 3M. According to claim 1, wherein the P-side electrode is at least one metal selected from the group consisting of tungsten (W), copper (Cu), molybdenum (Mo), gold (Au), and nickel (Ni) on a substrate Method of manufacturing a chalcogenide-based solar cell formed. The method of claim 5, wherein the substrate is glass, metal foil, metal tape, or plastic. The chalcogenide-based solar cell of claim 1, wherein the chalcogenide-based solar cell comprises a structure in which a chalcogenide-based compound thin film is bonded as a P-type semiconductor layer and an i-ZnO thin film is bonded as an N-type semiconductor layer. Manufacturing method. The method of manufacturing a chalcogenide-based solar cell according to claim 7, wherein a buffer layer is further interposed between the P-type semiconductor layer and the N-type semiconductor layer. A chalcogenide-based solar cell manufactured by the manufacturing method according to any one of claims 1 to 8.

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