KR101012565B1 - Solar cell having nanowires and nanoparticles and manufacturing method thereof - Google Patents

Abstract

Disclosed are a solar cell using nanowires as a hole transport layer or an electron transport layer, and nanoparticles as a photovoltaic layer and a method of manufacturing the same. The first nanoparticle layer formed on the lower electrode is used as an electron transport layer, and the second nanoparticle layer formed on the nanoparticle layer is used as a hole transport layer. Electrons and holes generated by sunlight incident on the nanoparticle layer, which is a photovoltaic layer, are transferred to the electron transfer layer and the hole transfer layer, respectively, and finally cause charge accumulation operations on the lower electrode and the upper electrode.

Solar cell, nanowire, nanoparticle, hybrid type

Description

Solar cell having nanowires and nanoparticles and method for manufacturing thereof {Solar Cell of having Nanowires and Nanoparticles, and Method of fabricating the same}

The present invention relates to a solar cell, and more particularly, to a solar cell manufactured using an organic material manufacturing process such as nanowires and nanoparticles electrochemical method and spin coating.

Recently, due to the limited reserves of fossil fuels, interest in new energy sources is increasing. In other words, interest in alternative energy sources is increasing worldwide, and efforts are being made to use wind, tidal, geothermal or solar energy as a new energy source.

In particular, solar cells are devices that directly convert solar energy into electrical energy using the photovoltaic effect. The basic operating principle of such a solar cell uses a p-n junction of a semiconductor. When sunlight with energy greater than the bandgap energy of the semiconductor is incident, electron-hole pairs are formed, and electrons and holes are separated into n- and p-layers by the electric field formed at the p-n junction, respectively, to generate photovoltaic power. At this time, when a load is connected to the electrodes at both ends of the solar cell, a current flows.

Solar cells have been commercialized with inorganic solar cells based on silicon, and research on this is being actively conducted. In addition, research on organic solar cells based on organic materials is actively underway. The main issues of this research will be the increase of photovoltaic efficiency and the reduction of manufacturing cost. Various types of solar cells have been proposed to improve photovoltaic efficiency. Among inorganic materials, compound semiconductor solar cells excluding silicon have been proposed, and research on organic solar cells is actively underway. In addition, various structures and production techniques have been proposed to reduce manufacturing costs.

Korean Unexamined Patent Publication No. 2008-97462 discloses an organic solar cell and a method of manufacturing the same. The disclosed patent forms a nanorod having an uneven structure as an electron transport layer, and arranges the nanoparticles on the nanorod. In addition, the separation space between the nanorods has a structure to fill the conductive polymer into the hole transport layer. At first glance, the disclosed patent may be judged as a simple manufacturing method, but has a problem of forming nanoparticles uniformly on the nanorods and a technical problem that is not easy in the process of embedding the conductive polymer through a solution process. In addition, it is necessary to form a conductive layer on top of the conductive polymer and to block it from the external environment. The use of a conductive polymer composed of an organic material as a hole transport layer results in a loss of stability and a decrease in photovoltaic efficiency. Occurs.

Korean Patent Laid-Open Publication No. 2008-73043 discloses a technical configuration in which carbon nanotubes are used as electron transfer materials, and a photovoltaic layer is a mixture of a hole acceptor and an electron acceptor. Although there is no description in the specification of the published patent, when judged by the disclosed configuration, an electron-hole pair is formed at the interface between the hole acceptor and the electron acceptor, electrons are transferred through carbon nanotubes, and holes are transported through ITO through the hole receptor. It is delivered to an anode made of transparent material. The disclosed patent is considered to have easy mass productivity because it has a relatively simple technical configuration, but the disadvantage of having a low light efficiency is exposed as the photoactive layer has a bulk heterocaption structure.

In order to solve the above problems, a first object of the present invention is to provide a solar cell using nanowires as an electron transport layer and a hole transport layer.

In addition, a second object of the present invention is to provide a method of manufacturing a solar cell used for achieving the first object.

The present invention for achieving the first object, the first nanowire layer for delivering holes to the lower electrode; A nanoparticle layer formed on the first nanowire layer to form an electron-hole pair by incidence of sunlight; And a second nanowire layer formed on the nanoparticle layer and configured to transfer holes formed in the nanoparticle layer to the upper electrode.

The present invention for achieving the second object, forming an n-type first nanowire layer on the substrate on which the lower electrode is formed; Forming a buffer layer exposing an upper region of the first nanowire layer in a space between the first nanowire layers; Forming a nanoparticle layer on the exposed upper region of the first nanowire layer; Forming a p-type second nanowire layer on the nanoparticle layer; And it provides a method for manufacturing a solar cell comprising the step of forming an upper electrode on the second nanowire layer.

According to the present invention described above, the nanoparticle layer which is a photoactive layer is interposed between the first nanowire layer and the second nanowire layer. In addition, the upper portion of the first nanowire layer to which the nanoparticle layer is attached has a structure exposed by the buffer layer for smooth contact with the second nanowire layer. Therefore, it is possible to secure a higher electron transfer rate and hole transfer degree than the conventional method of forming the electron transfer layer or the hole transfer layer as a bulk of the polymer, and the low manufacturing cost compared to the conventional process by forming the nanowire at a low temperature Can be secured.

As the inventive concept allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals are used for like elements in describing each drawing.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention.

Example

1 is a cross-sectional view showing a solar cell according to a preferred embodiment of the present invention.

Referring to FIG. 1, the solar cell according to the present exemplary embodiment includes a substrate 100, a lower electrode 110, a first nanowire layer 120, a buffer layer 135, a nanoparticle layer 140, and a second nanowire layer. 150 and the upper electrode 160.

First, the lower electrode 110 is formed on the transparent substrate 100, and the first nanowire layer 120 is formed on the lower electrode 110. Spaced spaces between the first nanowire layers 120 formed at predetermined intervals are filled with the buffer layer 135. The nanoparticle layer 140 is formed on the buffer layer 135 and on the surface of the first nanowire layer 120. A second nanowire layer 150 is provided on the nanoparticle layer 140, and an upper electrode 160 is formed on the second nanowire layer 150.

The first nanowire layer 120 has an n-type conductivity and functions as an electron accepting layer. The first nanowire layer 120 having a protruding shape on the lower electrode 110 forms a concave-convex structure on the surface of the lower electrode 110, and the space between the protruding nanowires is filled with the buffer layer 135. Is a structure. The first nanowire layer 120 is n-Si, n-Ge, n-SiC, n-CdS, n-CdSe, n-CdTe, ZnS, ZnSe, n-PbTe, n-AlAs, n-AlSb, n-GaAs, n-GaSb, n-GaP, n-InP, n-InSb, n-InAs, ZnO, GaN, GaAs, InP, CdS, CdSe, CdTe, ZnSe, ZnS, ZnTe, CdZnTe, SnO ₂ , TiO ₂ , consisting of silica or silica doped with gold. The first nanowire layer 120 receives electrons generated by absorption of sunlight and transmits them to the lower electrode 110.

The buffer layer 135 fills a space between the first nanowire layers 120. In addition, the buffer layer 135 may be any insulator, but preferably, a solution process may be possible, and a polymer insulator having a high gap fill capability of filling gaps between nanowires may be used. Accordingly, the buffer layer 135 may be made of polymethyl methacrylate (PMMA), polyvinylpyrrolidone (PVP), polystyrene (PS), or polyimide (PI). In addition, the buffer layer 135 is buried so that the upper portion of the first nanowire layer 120 is exposed without completely filling the first nanowire layer 120.

The nanoparticle layer 140 absorbs the incident sunlight and functions as a photovoltaic layer that generates electron-hole pairs. The nanoparticle layer 140 may be composed of semiconductor nanoparticles, oxide nanoparticles, or nanoparticles having a core / cell structure.

When the nanoparticle layer 140 is a semiconductor nanoparticle, it may be composed of Si, CdSe, ZnTe, ZnS, InP, ZnSe, GaAs, InGaAs, PbTe or PbS. In addition, when the nanoparticle layer 140 is an oxide nanoparticle, Al ₂ O ₃ , BaCO ₃ , Bi ₂ O ₃ , B ₂ O ₃ , CaCO ₃ , CeO ₂ , Cr ₂ O ₃ , CuO, Fe ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ , Li ₂ CO ₃ , LiCoO ₂ , MgO, MnCO ₃ , MnO ₂ , Mn ₃ O ₄ , Nb ₂ O ₅ , PbO, Sb ₂ O ₃ , SnO ₂ , SrCO ₃ , Ta ₂ O ₅ , TiO ₂ , BaTiO ₃ , V ₂ O ₅ , WO ₃ , ZrO ₂ , PbTiO ₃ , Pb _x Zr _{1 -x} TiO ₃ (0 <x <1) Or ZrTiO ₃ . In addition, when the nanoparticle layer 140 is a nanoparticle of the core / cell structure, CdSe (core) / ZnTe (cell) (hereinafter, in the same form), CdSe / ZnS, InP / ZnSe, InP / ZnS, InP / ZnTe, CdSe / ZnSe, InP / GaAs, InGaAs / GaAs, or PbTe / PbS.

The second nanowire layer 150 is provided on the nanoparticle layer 140. The second nanowire layer 150 has a p-type conductivity and functions as a hole acceptor. That is, it receives the holes generated in the nanoparticle layer 140, and transfers them to the upper electrode. The second nanowire layer 150 is p-Si, p-Ge, p-SiC, p-CdS, p-CdSe, p-CdTe, ZnS, ZnSe, p- PbTe, p-AlAs, p-AlSb, P-GaAs, p-GaSb, p-GaP, p-InP, p-InSb, p-InAs, Cu ₂ O or CuSCN is preferred.

In addition, a lower electrode 110 and an upper electrode 160 are provided on the substrate 100 on which the first nanowire layer 120, the nanoparticle layer 140, and the second nanowire layer 150 are formed.

The lower electrode 110 may be made of a transparent conductive material, and may be made of ITO, graphene, or carbon nanotubes. In addition, the upper electrode 160 may be made of a conductive metal material.

2 to 7 are cross-sectional views illustrating a method of manufacturing a solar cell according to a preferred embodiment of the present invention.

Referring to FIG. 2, the first nanowire layer 120 is formed on the substrate 100. Formation of the first nanowire layer 120 is accomplished by forming the lower electrode 110 on the substrate 100 and forming the first nanowire layer 120 on the formed lower electrode 110. .

For example, ITO is formed on the transparent substrate 100 by using the lower electrode 110, and the substrate 100 is washed with acetone, methanol, and deionized water to remove impurities on the lower electrode 110.

Subsequently, ZnO nanowires are grown vertically from the substrate 100 on the substrate 100 on which the ITO is formed by the electrochemical method to form the first nanowire layer 120. In other words, Zn (NO ₃ ) ₂ as a raw material and KCl are mixed and dissolved in deionized water as a solvent as a catalyst. At this time, Zn (NO ₃ ) ₂ is set to 1 mM to 10 mM, and KCl is fixed at 0.1M. Stir for 30 minutes using a spin bar to make a more uniform solution. In order to grow ZnO nanowires by electrochemical reaction in solution, three electrodes of a positive electrode, a negative electrode and a reference electrode are configured. The anode uses platinum, the cathode uses ITO, and the reference electrode uses Ag / AgCl. When the temperature of the solution is maintained at 65 ° C to 80 ° C and the voltage difference with the reference electrode is kept constant at -0.9V, single crystal ZnO nanowires grow in a direction perpendicular to the substrate. The length of the nanowires can be up to 700nm and the diameter can be formed from 20nm to several hundred nm.

Referring to FIG. 3, a buried layer 130 is formed on the substrate 100 on which the first nanowire layer 120 is formed. First, the buried layer 130 is preferably formed using a polymer solution process. That is, the buried layer 130 is formed by spin coating PMMA. PMMA is formed by filling the space between the formed nanowires. The buried layer 130 is a film quality corresponding to the previous step of the buffer layer 135 formed in FIG. 1, and the type of film quality is the same as that of the buffer layer 135. By forming the buried layer 130, the first nanowire layer 123 may not be exposed to the outside, and may be blocked from the outside by the buried layer 130.

Referring to FIG. 4, the upper region of the buried layer 130 is removed to expose the upper portion of the first nanowire layer 120. The buried layer 130 remaining by removing a portion of the buried layer 130 is referred to as a buffer layer 135. That is, the buffer layer 135 is formed by removing a portion of the buried layer 130 and has an aspect of exposing an upper portion of the first nanowire layer 120. Formation of the buffer layer 135 is accomplished by ashing on top of the buried layer 130 which completely fills the first nanowire layer 120.

Referring to FIG. 5, the nanoparticle layer 140 is formed in an upper region of the first nanowire layer 120 exposed by the buffer layer 135. For example, the nanoparticle layer 140 may be formed by applying an organic solvent such as toluene dispersed with CdSe nanoparticles by spin coating and evaporating the solvent. The nanoparticles forming the nanoparticle layer 140 are adsorbed onto the surface of the first nanowire layer 120.

6, a second nanowire layer 150 is formed on the formed nanoparticle layer 140. The second nanowire layer 150 is formed by an electrochemical method. For example, 0.4 M CuSO ₄ 5H ₂ O and ₃ M CH ₃ CH (OH) COOH are dissolved in deionized water. Subsequently, 5 M sodium hydroxide is added to the solution, followed by stirring for 24 hours using a spin rod. By stirring, the pH of the total solution is adjusted to 8. In addition, after setting the temperature of the solution to 60 ℃, maintaining the voltage difference with the reference electrode at -0.45V to obtain a single crystal Cu ₂ O nanowire grown vertically on the nanoparticle layer 140.

Referring to FIG. 7, the upper electrode 160 is formed on the second nanowire layer 150 formed of Cu ₂ O nanowires. The upper electrode 160 is preferably formed by using a method such as thermal evaporation Au.

2 to 7, the formation of the second nanowire layer 150 and the upper electrode 160 is shown to be formed on the pre-formed nanoparticle layer 140, this may be achieved by other manufacturing methods.

That is, after the upper electrode 160 is formed on another predetermined substrate, the second nanowire layer 150 is formed on the upper electrode 160. In addition, the lower electrode 110, the first nanowire layer 120, and the nanoparticle layer 140 are formed on the above-described transparent substrate. After forming each of the two structures separately, the substrate on which the second nanowire layer 150 is formed and the substrate on which the first nanowire layer 120 and the nanoparticle layer 140 are formed are bonded to each other. Solar cells can be manufactured. That is, the solar cell having the same structure as in FIG. 7 may be manufactured by combining the second nanowire layer 150 and the nanoparticle layer 140 formed separately.

In the present invention, the nanoparticle layer functions as a photovoltaic layer that absorbs sunlight to form electron-hole pairs. In addition, the first n-type nanowire layer in contact with the nanoparticle layer serves as an electron transporting layer that accepts electrons from the nanoparticle layer and transfers them to the lower electrode. Likewise, the second p-type nanowire layer acts as a hole transporting layer for transferring holes generated in the nanoparticle layer to the upper electrode. The above-described structure forms a p-i-n structure, and the p-type and n-type charge transport layers are composed of nanowires. The configuration with nanowires prevents electrons or holes from being lost by recombination in the bulk transport layer and increases light efficiency.

In addition, a solar cell can be easily manufactured without requiring high vacuum and high process temperature required by conventional molecular beam epitaxy (MBE) or organometallic chemical vapor deposition (MOCVD). Therefore, there is an advantage that can be produced a solar cell having a high light efficiency at a low cost.

1 is a cross-sectional view showing a solar cell according to a preferred embodiment of the present invention.

2 to 7 are cross-sectional views illustrating a method of manufacturing a solar cell according to a preferred embodiment of the present invention.

Claims (11)

A first nanowire layer for delivering holes to the lower electrode; A nanoparticle layer formed on the first nanowire layer to form an electron-hole pair by incidence of sunlight; And The solar cell is formed on the nanoparticle layer, comprising a second nanowire layer for transferring holes formed in the nanoparticle layer to the upper electrode. The method of claim 1, wherein the first nanowire layer has n-type conductivity, and n-Si, n-Ge, n-SiC, n-CdS, n-CdSe, n-CdTe, ZnS, ZnSe, n- PbTe, n-AlAs, n-AlSb, n-GaAs, n-GaSb, n-GaP, n-InP, n-InSb, n-InAs, ZnO, GaN, GaAs, InP, CdS, CdSe, CdTe, ZnSe, ZnS, ZnTe, CdZnTe, SnO ₂ , TiO ₂ , solar cells comprising gold or silica doped silica. The solar cell of claim 1, wherein the nanoparticle layer comprises semiconductor nanoparticles, oxide nanoparticles, or nanoparticles having a core / cell structure. The solar cell of claim 3, wherein the semiconductor nanoparticles are Si, CdSe, ZnTe, ZnS, InP, ZnSe, GaAs, InGaAs, PbTe, or PbS. The method of claim 3, wherein the oxide nanoparticles are Al ₂ O ₃ , BaCO ₃ , Bi ₂ O ₃ , B ₂ O ₃ , CaCO ₃ , CeO ₂ , Cr ₂ O ₃ , CuO, Fe ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ , Li ₂ CO ₃ , LiCoO ₂ , MgO, MnCO ₃ , MnO ₂ , Mn ₃ O ₄ , Nb ₂ O ₅ , PbO, Sb ₂ O ₃ , SnO ₂ , SrCO ₃ , Ta ₂ O ₅ , TiO ₂ , BaTiO ₃ , V ₂ O ₅ , WO ₃ , ZrO ₂ , PbTiO ₃ , Pb _x Zr _{1 -x} TiO ₃ (0 <x <1) Or ZrTiO ₃ solar cell. The method according to claim 3, wherein the core / cell nanoparticles are CdSe (core) / ZnTe (cell) (hereinafter, in the same form), CdSe / ZnS, InP / ZnSe, InP / ZnS, InP / ZnTe, CdSe / ZnSe, A solar cell, which is InP / GaAs, InGaAs / GaAs, or PbTe / PbS. The method of claim 1, wherein the second nanowire layer has a p-type conductivity, p-Si, p-Ge, p-SiC, p-CdS, p-CdSe, p-CdTe, ZnS, ZnSe, p- A solar cell comprising PbTe, p-AlAs, p-AlSb, p-GaAs, p-GaSb, p-GaP, p-InP, p-InSb, p-InAs, Cu ₂ O or CuSCN. The solar cell of claim 1, wherein the solar cell further comprises a buffer layer filling a space between the first nanowire layers and exposing an upper portion of the first nanowire layer. The solar cell of claim 8, wherein the buffer layer is an insulating polymer, and includes polymethyl methacrylate (PMMA), polyvinylpyrrolidone (PVP), polystyrene (PS), or polyimide (PI). The solar cell of claim 8, wherein the nanoparticle layer is formed on the first nanowire layer exposed by the buffer layer. Forming an n-type first nanowire layer on the substrate on which the lower electrode is formed; Forming a buffer layer exposing an upper region of the first nanowire layer in a space between the first nanowire layers; Forming a nanoparticle layer on the exposed upper region of the first nanowire layer; Forming a p-type second nanowire layer on the nanoparticle layer; And A method of manufacturing a solar cell comprising forming an upper electrode on the second nanowire layer.

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