WO2017150793A1 - Solar cell and fabrication method therefor - Google Patents

Solar cell and fabrication method therefor Download PDF

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Publication number
WO2017150793A1
WO2017150793A1 PCT/KR2016/014789 KR2016014789W WO2017150793A1 WO 2017150793 A1 WO2017150793 A1 WO 2017150793A1 KR 2016014789 W KR2016014789 W KR 2016014789W WO 2017150793 A1 WO2017150793 A1 WO 2017150793A1
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layer
buffer layer
solar cell
zns
buffer
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PCT/KR2016/014789
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French (fr)
Korean (ko)
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장승현
최우진
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주식회사 아바코
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Priority to CN201680071937.5A priority Critical patent/CN108401469B/en
Publication of WO2017150793A1 publication Critical patent/WO2017150793A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/036—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes
    • H01L31/0392—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes including thin films deposited on metallic or insulating substrates ; characterised by specific substrate materials or substrate features or by the presence of intermediate layers, e.g. barrier layers, on the substrate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/0445—PV modules or arrays of single PV cells including thin film solar cells, e.g. single thin film a-Si, CIS or CdTe solar cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/541—CuInSe2 material PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a solar cell and a method for manufacturing the same, and more particularly, to a thin film solar cell and a method for manufacturing the same that can improve the photoelectric conversion efficiency.
  • Solar cells are a key element in solar power generation that converts sunlight directly into electricity.
  • Solar cells can generally be classified into crystalline solar cells and thin film solar cells.
  • thin-film solar cells have lower energy conversion efficiency than crystalline solar cells, the thickness of the substrate can be significantly reduced, so the energy conversion efficiency per unit weight is much higher than that of crystalline solar cells.
  • the thin-film solar cell has been attracting attention because it can be manufactured as a flexible solar cell that can be deformed, and can be manufactured on an inexpensive substrate such as glass to reduce the cost.
  • a thin film solar cell includes a back electrode, a light absorber layer, a buffer layer, a window layer, and a front electrode sequentially formed on a substrate.
  • the light absorbing layer is mainly formed using a Cu (In, Ga) Se 2 (CIGS) compound semiconductor or a Cu 2 ZnSnSe 4 (CZTS) compound semiconductor.
  • a cadmium sulfide (CdS) layer formed through a wet process such as chemical bath deposition (CBD) is mainly used as a buffer layer.
  • CBD chemical bath deposition
  • the buffer layer in forming the buffer layer, development of Zn (O, S), ZnO: Mn (or Al, Cr, In), In 2 S 3 , and the like as a material to replace cadmium sulfide (CdS) is in progress.
  • the materials have advantages such as an increase in short-circuit current (Jsc) due to a wide band gap and an improvement in conversion efficiency, but a band offset due to a difference in Fermi energy level ( Due to Band Off-set and Lattice Mismatch, defects increase between the light absorbing layer, the buffer layer, and the window layer, thereby degrading efficiency.
  • the present invention has been made in view of such a problem, and the present invention provides a solar cell and a method of manufacturing the same, which can improve photoelectric conversion efficiency by reducing band offset and lattice mismatch between the light absorbing layer, the buffer layer, and the window layer. do.
  • a solar cell according to an aspect of the present invention is formed through an atomic layer deposition (ALD) process on the electrode layer formed on the substrate, the light absorbing layer formed on the electrode layer, the light absorbing layer, cadmium sulfide (CdS) and zinc sulfide (A first buffer layer formed by repeatedly stacking ZnS alternately, and a second formed by atomic layer deposition on the first buffer layer, and formed by alternately repeatedly depositing zinc oxide (ZnO) and zinc sulfide (ZnS). A buffer layer, and a window layer formed on the second buffer layer.
  • a first buffer layer formed by repeatedly stacking ZnS alternately
  • ZnO zinc oxide
  • ZnS zinc sulfide
  • ZnS zinc sulfide
  • the first buffer layer is Cd x Zn 1-x S, and x may be configured to 0.5 to 0.67.
  • the first buffer layer may be formed to a thickness of 10 ⁇ 20nm.
  • the second buffer layer may include S / (O + S), which is a composition ratio of sulfur (S) and oxygen (O), in a range of 10 to 25%.
  • the second buffer layer may be formed to a thickness of 10 to 20nm.
  • a method of manufacturing a solar cell including forming an electrode layer on a substrate, forming a light absorbing layer on the electrode layer, and performing an atomic layer deposition (ALD) process on the light absorbing layer.
  • ALD atomic layer deposition
  • CdS copper sulfide
  • ZnS zinc sulfide
  • ZnO zinc oxide
  • ZnS zinc sulfide
  • the first buffer layer is Cd x Zn 1 - x S, wherein x is 0.5 to 0.67, and may be formed to a thickness of 10 to 20 nm.
  • cadmium sulfide may be deposited before zinc sulfide.
  • the second buffer layer may have a composition ratio of sulfur (S) and oxygen (O) of S / (O + S) in a range of 10 to 25%, and may be formed to a thickness of 10 to 20 nm.
  • the first buffer layer and the second buffer layer may be formed at a temperature condition of 90 °C ⁇ 130 °C.
  • a first buffer layer in which cadmium sulfide (CdS) and zinc sulfide (ZnS) are alternately repeatedly stacked between the light absorbing layer and the window layer through an atomic layer deposition process, and zinc oxide By forming a second buffer layer in which ZnO) and zinc sulfide (ZnS) are alternately repeatedly stacked, the photoelectric conversion efficiency of the solar cell can be improved by reducing band offset and lattice mismatch between the light absorbing layer, the buffer layer, and the window layer.
  • FIG. 1 is a cross-sectional view showing a solar cell according to an embodiment of the present invention.
  • FIG. 2 is an enlarged cross-sectional view of the first buffer layer and the second buffer layer shown in FIG. 1.
  • 3 is a graph showing an X-ray diffraction pattern according to the change of material and composition ratio of the buffer layer.
  • FIG 4 is a band diagram of a solar cell using a Zn (O, S) single buffer layer and a solar cell using a first buffer layer of Cd x Zn 1 - x S and a second buffer layer of Zn (O, S). ).
  • FIG. 5 is a graph comparing module efficiency when the first and second buffer layers and the conventional cadmium buffer layer according to the present invention are used.
  • first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.
  • the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component.
  • FIG. 1 is a cross-sectional view illustrating a solar cell according to an exemplary embodiment of the present invention
  • FIG. 2 is an enlarged cross-sectional view of a first buffer layer and a second buffer layer shown in FIG. 1.
  • a solar cell 100 includes a substrate 110, an electrode layer 120 formed on the substrate 110, and a light absorbing layer formed on the electrode layer 120 ( 130, a first buffer layer 140 formed on the light absorbing layer 130, a second buffer layer 150 formed on the first buffer layer 140, and a window layer 160 formed on the second buffer layer 150. do.
  • the substrate 110 may be a substrate having various characteristics depending on the use.
  • the substrate 110 may use a transparent substrate, an opaque or translucent substrate, depending on the light transmission characteristics.
  • the substrate 110 may use a glass substrate, a ceramic substrate, a metal substrate, a polymer substrate, or the like depending on the material.
  • the substrate 110 may use a rigid substrate or a flexible substrate according to bending characteristics.
  • the substrate 110 may use a glass substrate having low light transmittance and low cost.
  • soda lime glass or high strained soda glass may be used as the glass substrate.
  • a substrate including stainless steel or titanium may be used as the metal substrate, and polyimide may be used as the polymer substrate.
  • the electrode layer 120 functions as a back electrode of the solar cell, and may be formed using a conductive material such as metal, and may be formed of a single layer or a plurality of layers of different materials.
  • the electrode layer 120 is preferably formed of a material having excellent adhesion to the substrate 110 so that the specific resistance is low and the peeling phenomenon does not occur due to the difference in the coefficient of thermal expansion.
  • the electrode layer 120 may be formed of chromium (Cr), molybdenum (Mo), an alloy of chromium and molybdenum.
  • the electrode layer 120 is preferably formed of molybdenum (Mo) having high electrical conductivity, excellent ohmic characteristics with the light absorbing layer 130, and excellent high temperature stability in a selenium (Se) atmosphere.
  • the electrode layer 120 may be formed by doping sodium (Na) ions to the conductive material.
  • the light absorbing layer 130 is formed on the electrode layer 120 and absorbs sunlight incident from the outside to generate electromotive force.
  • the light absorbing layer 130 may be formed of an I-III-VI compound or an I 2 -II-IV-VI 4 compound.
  • the group I elements include copper (Cu), the group II elements include zinc (Zn), the group III elements include indium (In), gallium (Ga), aluminum (Al), and the like.
  • Examples of tin (Sn) and group VI elements include selenium (Se) and sulfur (S).
  • the light absorbing layer 130 may be formed of a copper-indium-gallium-selenide (CuInGaSe 2 , CIGS) compound, or may be formed of a copper-zinc-tin-sulfur (Cu 2 ZnSnS 4 , CZTS) compound. .
  • CuInGaSe 2 copper-indium-gallium-selenide
  • Cu 2 ZnSnS 4 copper-zinc-tin-sulfur
  • the first buffer layer 140 is formed on the light absorbing layer 130 through an atomic layer deposition (ALD) process, and cadmium sulfide (CdS) 142 and zinc sulfide (ZnS) 144 are alternately repeatedly stacked. Is formed.
  • the first buffer layer 140 repeatedly stacks cadmium sulfide (CdS) 142 and zinc sulfide (ZnS) 144 on the P-type light absorbing layer 130 to have a bandgap energy (Eg) of 2.4 to 2.8.
  • Phosphorus Cd x Zn 1 - x S layer can be formed by Atomic Layer Deposition (ALD) process with easy control of thickness and composition (where x is a rational number between 0 and 1).
  • the composition ratio of cadmium (Cd) and zinc (Zn) contained in the first buffer layer 140 may be easily controlled by using an atomic layer deposition (ALD) process.
  • ALD atomic layer deposition
  • Photoelectric conversion efficiency can be improved by adjusting the composition ratio of Cd) and zinc (Zn). That is, by combining a specific composition ratio of Cd x Zn 1 - x S so that the lattice structures of the light absorbing layer 130 and the first buffer layer 140 are similar, the generation of defects at the interface due to lattice mismatch is reduced, thereby reducing photoelectric conversion efficiency. Can improve. This can be seen that the XRD peak is shifted according to the composition ratio of Cd x Zn 1-x S in FIG.
  • a is a buffer layer of CdS
  • b is Cd 0 . 67 a buffer layer of Zn 0 .33 S
  • c is 0 Cd. 5 Zn buffer of 0 .5 S
  • d is 0 Cd. 33
  • e is a buffer layer of ZnS
  • f denotes a buffer layer of a Zn (O, S)
  • g represents a CIGS-based light absorption layer.
  • X-ray diffraction (XRD) patterns are different from each other according to the material or composition ratio of the buffer layer.
  • the composition ratio of cadmium (Cd) and zinc (Zn) changes.
  • the XRD peak is shifted.
  • Cd x Zn 1 - x S buffer layer formed by repeatedly stacking CdS and ZnS (b)
  • c, d has an XRD peak similar to the XRD peak of the CIGS light absorbing layer (g).
  • Cd x Zn 1-x S buffer layers Cd 0 . 67 Zn 0 .33 S buffer layer (b), Cd 0.
  • Cd 0 .5 S buffer layer (c) that can be confirmed that the most similar XRD peaks and CIGS light absorption layer (g).
  • the buffer layer of Cd x Zn 1 - x S by configuring x to have a range of 0.5 ⁇ 0.67, it is possible to form the XRD peak of the buffer layer similar to the XRD peak of the CIGS light absorbing layer, thereby improving the photoelectric conversion efficiency Can be improved.
  • the photoelectric conversion efficiency of the solar cell 100 may vary depending on the thickness of the first buffer layer 140.
  • the highest photoelectric conversion efficiency may be obtained at a thickness of about 10 to 20 nm.
  • the second buffer layer 150 is formed through an atomic layer deposition process on the first buffer layer 140, and zinc oxide (ZnS) 152 and zinc sulfide (ZnS) 154 are alternately repeatedly formed. .
  • the second buffer layer 150 In forming the second buffer layer 150, by using an atomic layer deposition process, the composition ratio of sulfur (S) and oxygen (O) contained in the second buffer layer 150 can be easily adjusted, and sulfur (S) and Photoelectric conversion efficiency can be improved by adjusting the composition ratio of oxygen (O).
  • the second buffer layer 150 is formed of S / (O + S), which is a composition ratio of sulfur (S) and oxygen (O), in a range of about 10 to 25%, and has a thickness of about 10 to 20 nm. When the efficiency increase effect is maximized.
  • the second buffer layer 150 is continuously formed to mitigate lattice mismatch between the window layers 160 formed thereafter, and simultaneously generated electrons trap.
  • the photoelectric conversion efficiency can be improved by reducing the probability of
  • the material constituting the window layer 160 is mainly ZnO: B, it is possible to obtain an effect of growing well on the second ZnO-based second buffer layer 150 to lower the probability of peeling due to lattice mismatch.
  • FIG 4 is a band diagram of a solar cell using a Zn (O, S) single buffer layer and a solar cell using a first buffer layer of Cd x Zn 1 - x S and a second buffer layer of Zn (O, S). ).
  • a band offset with a P-type light absorbing layer may generate spikes or cliffs at an interface between two deposition surfaces, resulting in electrons. ) Or to hinder the flow of holes.
  • the first buffer layer of Cd x Zn 1 - x S and the second buffer layer of Zn (O, S) are used together, spikes or cliffs occur at the interface with the P-type light absorbing layer.
  • the flow of electrons and holes is smooth, and thus the probability of electron collection at the upper electrode is increased, thereby improving photoelectric conversion efficiency.
  • FIGS. 1 and 2 a method of manufacturing a solar cell according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
  • an electrode layer 120 is formed on a substrate 110.
  • the electrode layer 120 may be formed of, for example, chromium (Cr), molybdenum (Mo), an alloy of chromium and molybdenum, or the like, and may be formed by a method such as physical vapor deposition (PVD) or plating. have.
  • the light absorbing layer 130 is formed on the electrode layer 120.
  • the light absorbing layer 130 may include a copper-indium-gallium-selenide (CuInGaSe 2 , CIGS) compound, a copper-indium-selenide (CuInSe 2 , CIS) compound, or a copper-zinc-tin-sulfur (Cu 2 ZnSnS 4 , CZTS ) Compounds and the like.
  • the light absorbing layer 130 may be formed by various methods such as co-deposition, sputtering, and MOCVD. Among them, a sputtering method using copper, indium and gallium targets, respectively, or using a mixed target of copper, indium and gallium, sputtering on the electrode layer 120 on the electrode layer 120 (Cu, After the In, Ga; CIG) metal precursor (precursor) film is formed, a selenization process may be performed using selenium (Se) at a high temperature to form the light absorbing layer 130 of the CIGS compound.
  • the light absorbing layer 130 forms a second thin film layer made of a group VI element on the first thin film layer composed of at least one of group I and group III elements, and then performs the heat treatment process to form the first thin film layer and the first layer.
  • the light absorbing layer 130 may be formed by reacting the 2 thin film layers.
  • the first thin film layer may be formed of an indium, copper, gallium thin film layer, an alloy of two elements and a thin film layer of one element, or may be formed of an alloy of three elements, and the second thin film layer is formed of at least one of selenium and sulfur. can do.
  • the first thin film layer may be made of Cu / Ga / In, Cu-In alloy / Ga, Cu-Ga alloy / In, Ca-In alloy / Cu, Cu-Ga-In alloy, and the second thin film layer It may consist of Se, S or Se / S.
  • the first thin film layer and the second thin film layer may be reacted by a heat treatment process to form a light absorbing layer 130 such as CGS, CIS, CIGS, or the like.
  • the manufacturing process of the light absorbing layer 130 composed of a copper-zinc-tin-sulfur (Cu 2 ZNSnS 4 , CZTS) compound is also very similar to that of manufacturing a CIGS light absorbing layer, and a thin film precursor of copper-zinc-tin is mainly It may be formed, and sulfation (sulfization) to prepare a CZTS light absorbing layer.
  • a copper-zinc-tin-sulfur (Cu 2 ZNSnS 4 , CZTS) compound is also very similar to that of manufacturing a CIGS light absorbing layer, and a thin film precursor of copper-zinc-tin is mainly It may be formed, and sulfation (sulfization) to prepare a CZTS light absorbing layer.
  • cadmium sulfide (CdS) and zinc sulfide (ZnS) are alternately repeatedly stacked on the light absorbing layer 130 to form a first buffer layer 140.
  • zinc oxide (ZnO) and zinc sulfide (ZnS) are alternately repeatedly stacked on the first buffer layer 140 to form a second buffer layer 150.
  • the first buffer layer 140 and the second buffer layer 150 are formed by an atomic layer deposition (ALD) process that is dry and easy to control thickness and composition.
  • ALD atomic layer deposition
  • the first buffer layer 140 and the second buffer layer 150 are formed by successive deposition in one ALD device.
  • the first buffer layer 140 and the second buffer layer 150 may be made of dimethyl cadmium (DMCd), diethyl zinc (DEZn), H 2 O, H 2 S and the like can be used as a precursor.
  • DMCd dimethyl cadmium
  • DEZn diethyl zinc
  • H 2 O H 2 S and the like
  • N 2 or Ar is used as the purge gas
  • the process pressure is preferably formed at a condition of about 0.1 to 2.0 torr.
  • the temperature of the canister for evaporating dimethyl cadmium (DMCd) and diethyl zinc (DEZn) sources ranges from 5 to 40 ° C.
  • the first buffer layer 140 and the second buffer layer 150 are formed of cadmium sulfide (CdS) 142, zinc sulfide (ZnS) 144, zinc oxide (ZnO), and zinc sulfide (ZnS) as a monolayer.
  • the composition ratio can be adjusted by repeatedly forming one layer and one layer.
  • the first buffer layer 140 made of Cd x Zn 1 - x S has x in a range of 0.5 to 0.67, a thickness of 10 to 20 nm, and Zn
  • the second buffer layer 150 made of (O, S) has a composition ratio of S / (O + S) of 10 to 25%, and a thickness of 10 to 20 nm.
  • cadmium sulfide (CdS) before zinc sulfide (ZnS). This is because the lattice parameter of cadmium sulfide (CdS) is more similar than that of zinc sulfide (ZnS) compared to the lattice parameter of the light absorbing layer 130.
  • the lattice parameter of the light absorbing layer of CIGS is 5.8 mW
  • the lattice parameter of cadmium sulfide (CdS) is 5.83 mW
  • the lattice parameter of zinc sulfide (ZnS) is 5.42 mW.
  • the deposition order of the first buffer layer 140 and the second buffer layer 150 using the atomic layer deposition (ALD) method is source (DMCd, DEZn) feeding-N 2 purge-source (H 2 O, H 2 S ) Feeding-consists of four stages of N 2 purge and are independent processes.
  • the first buffer layer 140 and the second buffer layer 150 may be formed to several tens of atomic layers by repeating the above-described four cycles of the first cycle a plurality of times.
  • the process temperatures of cadmium sulfide (CdS), zinc sulfide (ZnS), and zinc oxide (ZnO) are different from each other. It is preferable to form on the temperature conditions of ° C-130 ° C.
  • the process temperature is higher than the above conditions, the desorption and desorption of the surface ligand that activates the surface for the next reaction or desorption of the formed monolayer not only results in a thin film of the desired quality, but also has a low growth per cycle (GPC).
  • GPC growth per cycle
  • the mixed buffer layer 140 by depositing one layer and one layer in a monolayer through the atomic layer deposition (ALD) method, defects in the thin film are reduced, and electrons generated by the photoreaction are trapped as they pass through the buffer layer. can reduce the probability of being trapped.
  • ALD atomic layer deposition
  • a window layer 160 made of a transparent conductive material is formed on the second buffer layer 150.
  • the window layer 160 may be formed by, for example, doping aluminum (Al) or boron (B) with zinc oxide (ZnO).
  • the window layer 160 may be formed through an organometallic chemical vapor deposition (MOCVD) process or a sputtering process.
  • MOCVD organometallic chemical vapor deposition
  • the window layer 160 supplies a zinc (Zn) source, an oxygen (O 2 ) source, and a dopant gas (for example, B 2 H 6 ) at the same time to ZnO in an organometallic chemical vapor deposition (MOCVD) process.
  • a B layer can be formed.
  • the window layer 160 may be formed of a ZnO: Al layer by a sputtering process targeting ZnO: Al 2 O 3 and using a Zn: Al target in an argon (Ar) + oxygen (O 2 ) atmosphere.
  • a ZnO: Al layer can also be formed.
  • FIG. 5 is a graph comparing module efficiency when the first and second buffer layers and the conventional cadmium buffer layer according to the present invention are used.
  • the double buffer layer structure including the first buffer layer 140 of Cd x Zn 1 - x S and the second buffer layer 150 of Zn (O, S) is used as in the exemplary embodiment of the present invention.
  • the module efficiency is improved.

Abstract

The present invention provides a solar cell capable of enhancing photoelectric conversion efficiency and a method for fabricating the same. The solar cell according to the present invention comprises: an electrode layer formed on a substrate; a light absorber layer formed on the electrode layer; a first buffer layer formed on the light absorber layer by an atomic layer deposition (ALD) process in which cadmium sulfide (CdS) and zinc sulfide (ZnS)are repeatedly deposited in an alternating manner; a second buffer layer formed on the first buffer layer by an atomic layer deposition process in which zinc oxide (ZnO) and zinc sulfide (ZnS) are repeatedly deposited in an alternating manner; and a window layer formed on the second buffer layer. As such, formation of the first buffer layer having cadmium sulfide (CdS) and zinc sulfide (ZnS) deposited repeatedly and alternatingly therein and the second buffer layer having zinc oxide (ZnO) and zinc sulfide (ZnS) deposited repeatedly and alternatingly therein between the light absorber layer and the window layer through an atomic layer deposition process reduces band offsets and lattice mismatches among the light absorber layer, the buffer layers, and the window layer, thus enhancing the photoelectric conversion efficiency of the solar cell.

Description

태양 전지 및 이의 제조 방법Solar cell and manufacturing method thereof
본 발명은 태양 전지 및 이의 제조 방법에 관한 것으로, 더욱 상세하게는 광전 변환 효율을 향상시킬 수 있는 박막형 태양 전지 및 이의 제조 방법에 관한 것이다.The present invention relates to a solar cell and a method for manufacturing the same, and more particularly, to a thin film solar cell and a method for manufacturing the same that can improve the photoelectric conversion efficiency.
태양 전지(solar cell)는 태양광을 직접 전기로 변환시키는 태양광 발전의 핵심 소자이다. 태양 전지는 일반적으로 결정계 태양 전지와 박막형 태양 전지로 분류될 수 있다. 박막형 태양 전지는 결정계 태양 전지에 비해 에너지 변환 효율은 낮지만, 기판의 두께를 혁신적으로 줄일 수 있어 단위 무게당 에너지 변환 효율은 결정계 태양 전지보다 훨씬 높은 편이다. 뿐만 아니라, 박막형 태양 전지는 변형이 가능한 유연 태양 전지로 제작이 가능하고, 유리 등의 저렴한 기판 상에 제조하여 저가화할 수 있는 등 많은 장점이 있어 주목을 받고 있다. Solar cells are a key element in solar power generation that converts sunlight directly into electricity. Solar cells can generally be classified into crystalline solar cells and thin film solar cells. Although thin-film solar cells have lower energy conversion efficiency than crystalline solar cells, the thickness of the substrate can be significantly reduced, so the energy conversion efficiency per unit weight is much higher than that of crystalline solar cells. In addition, the thin-film solar cell has been attracting attention because it can be manufactured as a flexible solar cell that can be deformed, and can be manufactured on an inexpensive substrate such as glass to reduce the cost.
일반적으로, 박막형 태양 전지는 기판 상에 순차적으로 형성된 후면 전극층(back electrode), 광 흡수층(absorber layer), 버퍼층(buffer layer), 윈도우층(window layer) 및 전면 전극(front electrode)을 포함한다. 여기서, 상기 광 흡수층은 주로 Cu(In,Ga)Se2(CIGS) 화합물 반도체 또는 Cu2ZnSnSe4(CZTS) 화합물 반도체를 이용하여 형성된다. In general, a thin film solar cell includes a back electrode, a light absorber layer, a buffer layer, a window layer, and a front electrode sequentially formed on a substrate. Here, the light absorbing layer is mainly formed using a Cu (In, Ga) Se 2 (CIGS) compound semiconductor or a Cu 2 ZnSnSe 4 (CZTS) compound semiconductor.
CIGS계 박막 태양 전지의 경우, 버퍼층으로는 화학 용액 증착법(chemical bath deposition: CBD) 등의 습식 공정을 통해 형성한 황화카드뮴(CdS)층이 주로 이용되고 있다. 그러나, 화학 용액 증착법 등의 습식 공정을 이용하는 경우 독성이 높은 황화카드뮴(CdS)과 알칼리성 폐액이 대량으로 생성되기 때문에 환경 오염의 염려가 있고, 그에 따른 폐기물 처리 비용이 증가하여 태양 전지의 제조 비용이 증가하는 문제가 있다. In the case of CIGS-based thin film solar cells, a cadmium sulfide (CdS) layer formed through a wet process such as chemical bath deposition (CBD) is mainly used as a buffer layer. However, when a wet process such as a chemical solution deposition method is used, a large amount of highly toxic cadmium sulfide (CdS) and an alkaline waste solution are generated, which may cause environmental pollution, resulting in increased waste disposal costs, thereby increasing the cost of manufacturing solar cells. There is a growing problem.
이에 따라, 상기 버퍼층을 형성함에 있어, 황화카드뮴(CdS)을 대체하는 물질로 Zn(O,S), ZnO:Mn(or Al, Cr, In), In2S3 등의 개발이 진행되고 있다. 그러나, 상기 물질들의 경우, 와이드 밴드 갭(wide band gap)으로 인한 단락전류밀도(Jsc : Short-circuit current)의 증가, 변환 효율 향상 등의 장점이 있으나, 페르미 에너지 레벨의 차이로 인한 밴드 옵셋(Band Off-set) 및 격자 부정합(Lattice Mismatch)으로 인해 광 흡수층, 버퍼층 및 윈도우층의 사이에 결함(Defect)이 증가하여 효율을 저하시키는 문제가 있다. Accordingly, in forming the buffer layer, development of Zn (O, S), ZnO: Mn (or Al, Cr, In), In 2 S 3 , and the like as a material to replace cadmium sulfide (CdS) is in progress. . However, the materials have advantages such as an increase in short-circuit current (Jsc) due to a wide band gap and an improvement in conversion efficiency, but a band offset due to a difference in Fermi energy level ( Due to Band Off-set and Lattice Mismatch, defects increase between the light absorbing layer, the buffer layer, and the window layer, thereby degrading efficiency.
따라서, 본 발명은 이와 같은 문제점을 감안한 것으로써, 본 발명은 광 흡수층, 버퍼층 및 윈도우층 사이의 밴드 옵셋 및 격자 부정합을 감소시켜, 광전 변환 효율을 향상시킬 수 있는 태양 전지 및 이의 제조 방법을 제공한다. Accordingly, the present invention has been made in view of such a problem, and the present invention provides a solar cell and a method of manufacturing the same, which can improve photoelectric conversion efficiency by reducing band offset and lattice mismatch between the light absorbing layer, the buffer layer, and the window layer. do.
본 발명의 일 특징에 따른 태양 전지는 기판 상에 형성된 전극층, 상기 전극층 상에 형성된 광 흡수층, 상기 광 흡수층 상에 원자층 증착(ALD) 공정을 통해 형성되며, 황화카드뮴(CdS)과 황화아연(ZnS)이 교대로 반복적으로 적층되어 형성된 제1 버퍼층, 상기 제1 버퍼층 상에 원자층 증착 공정을 통해 형성되며, 산화아연(ZnO)과 황화아연(ZnS)이 교대로 반복적으로 적층되어 형성된 제2 버퍼층, 및 상기 제2 버퍼층 상에 형성된 윈도우층을 포함한다. A solar cell according to an aspect of the present invention is formed through an atomic layer deposition (ALD) process on the electrode layer formed on the substrate, the light absorbing layer formed on the electrode layer, the light absorbing layer, cadmium sulfide (CdS) and zinc sulfide ( A first buffer layer formed by repeatedly stacking ZnS alternately, and a second formed by atomic layer deposition on the first buffer layer, and formed by alternately repeatedly depositing zinc oxide (ZnO) and zinc sulfide (ZnS). A buffer layer, and a window layer formed on the second buffer layer.
상기 제1 버퍼층은 CdxZn1-xS이며, 상기 x는 0.5 ~ 0.67로 구성될 수 있다.The first buffer layer is Cd x Zn 1-x S, and x may be configured to 0.5 to 0.67.
상기 제1 버퍼층은 10 ~ 20nm의 두께로 형성될 수 있다. The first buffer layer may be formed to a thickness of 10 ~ 20nm.
상기 제2 버퍼층은 황(S)과 산소(O)의 조성비인 S/(O+S)가 10 ~ 25%의 범위로 구성될 수 있다. The second buffer layer may include S / (O + S), which is a composition ratio of sulfur (S) and oxygen (O), in a range of 10 to 25%.
상기 제2 버퍼층은 10 ~ 20nm의 두께로 형성될 수 있다.The second buffer layer may be formed to a thickness of 10 to 20nm.
본 발명의 다른 특징에 따른 태양 전지의 제조 방법은, 기판 상에 전극층을 형성하는 단계, 상기 전극층 상에 광 흡수층을 형성하는 단계, 상기 광 흡수층 상에 원자층 증착(ALD) 공정을 통해 황화카드뮴(CdS)과 황화아연(ZnS)을 교대로 반복적으로 적층하여 제1 버퍼층을 형성하는 단계, 상기 제1 버퍼층 상에 원자층 증착 공정을 통해 산화아연(ZnO)과 황화아연(ZnS)을 교대로 반복적으로 적층하여 제2 버퍼층을 형성하는 단계, 및 상기 제2 버퍼층 상에 윈도우층을 형성하는 단계를 포함한다.According to another aspect of the present invention, there is provided a method of manufacturing a solar cell, including forming an electrode layer on a substrate, forming a light absorbing layer on the electrode layer, and performing an atomic layer deposition (ALD) process on the light absorbing layer. Alternately repeatedly stacking (CdS) and zinc sulfide (ZnS) to form a first buffer layer, and alternately alternate zinc oxide (ZnO) and zinc sulfide (ZnS) through an atomic layer deposition process on the first buffer layer. Stacking repeatedly to form a second buffer layer, and forming a window layer on the second buffer layer.
상기 제1 버퍼층은 CdxZn1 - xS이며, 상기 x는 0.5 ~ 0.67로 구성되고, 10 ~ 20nm의 두께로 형성될 수 있다. The first buffer layer is Cd x Zn 1 - x S, wherein x is 0.5 to 0.67, and may be formed to a thickness of 10 to 20 nm.
상기 제1 버퍼층을 형성함에 있어, 황화카드뮴을 황화아연보다 먼저 증착할 수 있다.In forming the first buffer layer, cadmium sulfide may be deposited before zinc sulfide.
상기 제2 버퍼층은 황(S)과 산소(O)의 조성비인 S/(O+S)가 10 ~ 25%의 범위로 구성되고, 10 ~ 20nm의 두께로 형성될 수 있다.The second buffer layer may have a composition ratio of sulfur (S) and oxygen (O) of S / (O + S) in a range of 10 to 25%, and may be formed to a thickness of 10 to 20 nm.
상기 제1 버퍼층 및 제2 버퍼층은 90℃ ~ 130℃의 온도 조건에서 형성될 수 있다.The first buffer layer and the second buffer layer may be formed at a temperature condition of 90 ℃ ~ 130 ℃.
이와 같은 태양 전지 및 이의 제조 방법에 따르면, 광 흡수층과 윈도우층 사이에 원자층 증착 공정을 통해 황화카드뮴(CdS)과 황화아연(ZnS)이 교대로 반복적으로 적층된 제1 버퍼층과, 산화아연(ZnO)과 황화아연(ZnS)이 교대로 반복적으로 적층된 제2 버퍼층을 형성함으로써, 광 흡수층, 버퍼층 및 윈도우층 사이의 밴드 옵셋 및 격자 부정합을 감소시켜 태양 전지의 광전 변환 효율을 향상시킬 수 있다.According to such a solar cell and a method of manufacturing the same, a first buffer layer in which cadmium sulfide (CdS) and zinc sulfide (ZnS) are alternately repeatedly stacked between the light absorbing layer and the window layer through an atomic layer deposition process, and zinc oxide ( By forming a second buffer layer in which ZnO) and zinc sulfide (ZnS) are alternately repeatedly stacked, the photoelectric conversion efficiency of the solar cell can be improved by reducing band offset and lattice mismatch between the light absorbing layer, the buffer layer, and the window layer. .
도 1은 본 발명의 일 실시예에 따른 태양 전지를 나타낸 단면도이다.1 is a cross-sectional view showing a solar cell according to an embodiment of the present invention.
도 2는 도 1에 도시된 제1 버퍼층 및 제2 버퍼층을 확대한 단면도이다.FIG. 2 is an enlarged cross-sectional view of the first buffer layer and the second buffer layer shown in FIG. 1.
도 3은 버퍼층의 물질 및 조성비 변화에 따른 X-선 회절 패턴을 나타낸 그래프이다. 3 is a graph showing an X-ray diffraction pattern according to the change of material and composition ratio of the buffer layer.
도 4는 Zn(O,S) 단일 버퍼층을 사용한 태양전지와, CdxZn1 - xS의 제1 버퍼층과 Zn(O,S)의 제2 버퍼층을 같이 사용한 태양전지의 밴드 다이어그램(Band Diagram)을 비교한 도면이다.4 is a band diagram of a solar cell using a Zn (O, S) single buffer layer and a solar cell using a first buffer layer of Cd x Zn 1 - x S and a second buffer layer of Zn (O, S). ).
도 5는 본 발명에 따른 제1 및 제2 버퍼층과 기존의 카드뮴 버퍼층을 사용한 경우의 모듈 효율을 비교한 그래프이다.5 is a graph comparing module efficiency when the first and second buffer layers and the conventional cadmium buffer layer according to the present invention are used.
본 발명은 다양한 변경을 가할 수 있고 여러 가지 형태를 가질 수 있는 바, 특정 실시예들을 도면에 예시하고 본문에 상세하게 설명하고자 한다. 그러나, 이는 본 발명을 특정한 개시 형태에 대해 한정하려는 것이 아니며, 본 발명의 사상 및 기술 범위에 포함되는 모든 변경, 균등물 내지 대체물을 포함하는 것으로 이해되어야 한다.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.
제1, 제2 등의 용어는 다양한 구성 요소들을 설명하는데 사용될 수 있지만, 상기 구성 요소들은 상기 용어들에 의해 한정되어서는 안된다. 상기 용어들은 하나의 구성 요소를 다른 구성 요소로부터 구별하는 목적으로만 사용된다. 예를 들어, 본 발명의 권리 범위를 벗어나지 않으면서 제1 구성 요소는 제2 구성 요소로 명명될 수 있고, 유사하게 제2 구성 요소도 제1 구성 요소로 명명될 수 있다. Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component.
본 출원에서 사용한 용어는 단지 특정한 실시예들을 설명하기 위해 사용된 것으로, 본 발명을 한정하려는 의도가 아니다. 단수의 표현은 문맥상 명백하게 다르게 뜻하지 않는 한, 복수의 표현을 포함한다. 본 출원에서, "포함하다" 또는 "가지다" 등의 용어는 명세서에 기재된 특징, 숫자, 단계, 동작, 구성 요소, 부분품 또는 이들을 조합한 것이 존재함을 지정하려는 것이지, 하나 또는 그 이상의 다른 특징들이나 숫자, 단계, 동작, 구성 요소, 부분품 또는 이들을 조합한 것들의 존재 또는 부가 가능성을 미리 배제하지 않는 것으로 이해되어야 한다.The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "having" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof described in the specification, and that one or more other features It should be understood that it does not exclude in advance the possibility of the presence or addition of numbers, steps, actions, components, parts or combinations thereof.
다르게 정의되지 않는 한, 기술적이거나 과학적인 용어를 포함해서 여기서 사용되는 모든 용어들은 본 발명이 속하는 기술 분야에서 통상의 지식을 가진 자에 의해 일반적으로 이해되는 것과 동일한 의미를 갖는다.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.
일반적으로 사용되는 사전에 정의되어 있는 것과 같은 용어들은 관련 기술의 문맥상 가지는 의미와 일치하는 의미를 갖는 것으로 해석되어야 하며, 본 출원에서 명백하게 정의하지 않는 한, 이상적이거나 과도하게 형식적인 의미로 해석되지 않는다.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.
이하, 첨부한 도면들을 참조하여, 본 발명의 바람직한 실시예들을 보다 상세하게 설명한다.Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.
도 1은 본 발명의 일 실시예에 따른 태양 전지를 나타낸 단면도이며, 도 2는 도 1에 도시된 제1 버퍼층 및 제2 버퍼층을 확대한 단면도이다.1 is a cross-sectional view illustrating a solar cell according to an exemplary embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view of a first buffer layer and a second buffer layer shown in FIG. 1.
도 1 및 도 2를 참조하면, 본 발명의 일 실시예에 따른 태양 전지(100)는 기판(110), 기판(110) 상에 형성된 전극층(120), 전극층(120) 상에 형성된 광 흡수층(130), 광 흡수층(130) 상에 형성된 제1 버퍼층(140), 제1 버퍼층(140) 상에 형성된 제2 버퍼층(150) 및 제2 버퍼층(150) 상에 형성된 윈도우층(160)을 포함한다. 1 and 2, a solar cell 100 according to an embodiment of the present invention includes a substrate 110, an electrode layer 120 formed on the substrate 110, and a light absorbing layer formed on the electrode layer 120 ( 130, a first buffer layer 140 formed on the light absorbing layer 130, a second buffer layer 150 formed on the first buffer layer 140, and a window layer 160 formed on the second buffer layer 150. do.
기판(110)은 용도에 따라 다양한 특성의 기판이 사용될 수 있다. 예를 들어, 기판(110)은 광 투과 특성에 따라 투명 기판, 불투명 또는 반투명 기판을 이용할 수 있다. 또한, 기판(110)은 재질에 따라 유리 기판, 세라믹 기판, 금속 기판, 폴리머 기판 등을 이용할 수 있다. 또한, 기판(110)은 굽힘 특성에 따라 리지드(rigid) 기판 또는 플렉서블(flexible) 기판을 이용할 수 있다. 바람직하게, 기판(110)은 광 투과성을 가지며 비용이 저렴한 유리 기판을 이용할 수 있다. 유리 기판으로는 예를 들어, 소다라임 유리(sodalime glass) 또는 고변형점 소다유리(high strained point soda glass)를 이용할 수 있다. 한편, 금속 기판으로는 스테인레스 스틸 또는 티타늄을 포함하는 기판을 이용할 수 있고, 폴리머 기판으로는 폴리이미드(polyimide)를 이용할 수 있다.The substrate 110 may be a substrate having various characteristics depending on the use. For example, the substrate 110 may use a transparent substrate, an opaque or translucent substrate, depending on the light transmission characteristics. In addition, the substrate 110 may use a glass substrate, a ceramic substrate, a metal substrate, a polymer substrate, or the like depending on the material. In addition, the substrate 110 may use a rigid substrate or a flexible substrate according to bending characteristics. Preferably, the substrate 110 may use a glass substrate having low light transmittance and low cost. For example, soda lime glass or high strained soda glass may be used as the glass substrate. Meanwhile, a substrate including stainless steel or titanium may be used as the metal substrate, and polyimide may be used as the polymer substrate.
전극층(120)은 태양 전지의 이면 전극 기능을 하는 것으로, 금속 등의 도전 물질을 이용하여 형성될 수 있으며, 단일층 또는 서로 다른 물질의 복수의 층으로 형성될 수 있다. 전극층(120)은 비저항이 낮으면서, 열팽창 계수의 차이로 인해 기판(110)과 박리 현상이 일어나지 않도록 기판(110)과의 점착성이 뛰어난 물질로 형성되는 것이 바람직하다. 예를 들어, 전극층(120)은 크롬(Cr), 몰리브덴(Mo), 크롬과 몰리브덴의 합금으로 형성될 수 있다. 특히, 전극층(120)은 전기 전도도가 높고, 광 흡수층(130)과의 오믹(ohmic) 특성이 우수하며, 셀레늄(Se) 분위기에서의 고온 안정성이 뛰어난 몰리브덴(Mo)으로 형성되는 것이 바람직하다. 또한, 전극층(120)은 도전 물질에 나트륨(Na) 이온이 도핑되어 형성될 수도 있다.The electrode layer 120 functions as a back electrode of the solar cell, and may be formed using a conductive material such as metal, and may be formed of a single layer or a plurality of layers of different materials. The electrode layer 120 is preferably formed of a material having excellent adhesion to the substrate 110 so that the specific resistance is low and the peeling phenomenon does not occur due to the difference in the coefficient of thermal expansion. For example, the electrode layer 120 may be formed of chromium (Cr), molybdenum (Mo), an alloy of chromium and molybdenum. In particular, the electrode layer 120 is preferably formed of molybdenum (Mo) having high electrical conductivity, excellent ohmic characteristics with the light absorbing layer 130, and excellent high temperature stability in a selenium (Se) atmosphere. In addition, the electrode layer 120 may be formed by doping sodium (Na) ions to the conductive material.
광 흡수층(130)은 전극층(120) 상에 형성되며, 외부로부터 입사되는 태양광을 흡수하여 기전력을 발생시킨다. 광 흡수층(130)은 Ⅰ-Ⅲ-Ⅵ계 화합물 또는 I2-Ⅱ-Ⅳ-Ⅵ4계 화합물로 형성될 수 있다. 여기서, Ⅰ족 원소로는 구리(Cu), Ⅱ족 원소로는 아연(Zn), Ⅲ족 원소로는 인듐(In), 갈륨(Ga), 알루미늄(Al) 등을 들 수 있으며, Ⅳ족 원소로는 틴(Sn), Ⅵ족 원소로는 셀렌(Se) 또는 황(S)을 들 수 있다. 예를 들어, 광 흡수층(130)은 구리-인듐-갈륨-셀레나이드(CuInGaSe2, CIGS) 화합물로 형성되거나, 구리-아연-틴-황(Cu2ZnSnS4, CZTS) 화합물로 형성될 수 있다. The light absorbing layer 130 is formed on the electrode layer 120 and absorbs sunlight incident from the outside to generate electromotive force. The light absorbing layer 130 may be formed of an I-III-VI compound or an I 2 -II-IV-VI 4 compound. The group I elements include copper (Cu), the group II elements include zinc (Zn), the group III elements include indium (In), gallium (Ga), aluminum (Al), and the like. Examples of tin (Sn) and group VI elements include selenium (Se) and sulfur (S). For example, the light absorbing layer 130 may be formed of a copper-indium-gallium-selenide (CuInGaSe 2 , CIGS) compound, or may be formed of a copper-zinc-tin-sulfur (Cu 2 ZnSnS 4 , CZTS) compound. .
제1 버퍼층(140)은 광 흡수층(130) 상에 원자층 증착(ALD) 공정을 통해 형성되며, 황화카드뮴(CdS)(142)과 황화아연(ZnS)(144)이 교대로 반복적으로 적층되어 형성된다. 제1 버퍼층(140)은 P-type의 광 흡수층(130) 상에 황화카드뮴(CdS)(142)과 황화아연(ZnS)(144)을 반복적으로 적층하여 밴드갭 에너지(Eg)가 2.4 ~ 2.8인 CdxZn1 - xS 층을 두께나 조성의 조절이 용이한 원자층 증착(Atomic Layer Deposition : ALD) 공정으로 형성될 수 있다.(여기서, x는 0과 1 사이의 유리수이다)The first buffer layer 140 is formed on the light absorbing layer 130 through an atomic layer deposition (ALD) process, and cadmium sulfide (CdS) 142 and zinc sulfide (ZnS) 144 are alternately repeatedly stacked. Is formed. The first buffer layer 140 repeatedly stacks cadmium sulfide (CdS) 142 and zinc sulfide (ZnS) 144 on the P-type light absorbing layer 130 to have a bandgap energy (Eg) of 2.4 to 2.8. Phosphorus Cd x Zn 1 - x S layer can be formed by Atomic Layer Deposition (ALD) process with easy control of thickness and composition (where x is a rational number between 0 and 1).
제1 버퍼층(140)을 형성함에 있어, 원자층 증착(ALD) 공정을 이용함으로써 제1 버퍼층(140) 내에 함유된 카드뮴(Cd)과 아연(Zn)의 조성비를 용이하게 조절할 수 있으며, 카드뮴(Cd)과 아연(Zn)의 조성비를 조절함으로써 광전 변환 효율을 향상시킬 수 있다. 즉, 광 흡수층(130)과 제1 버퍼층(140)의 격자 구조가 유사해지도록 CdxZn1 - xS의 특정 조성비를 조합함으로써 격자 부정합에 의해 계면에서 결함이 발생하는 것을 감소시켜 광전 변환 효율을 향상시킬 수 있다. 이는 도 3에서 CdxZn1-xS의 조성비에 따라 XRD 피크가 쉬프트되는 것으로 확인할 수 있다.In forming the first buffer layer 140, the composition ratio of cadmium (Cd) and zinc (Zn) contained in the first buffer layer 140 may be easily controlled by using an atomic layer deposition (ALD) process. Photoelectric conversion efficiency can be improved by adjusting the composition ratio of Cd) and zinc (Zn). That is, by combining a specific composition ratio of Cd x Zn 1 - x S so that the lattice structures of the light absorbing layer 130 and the first buffer layer 140 are similar, the generation of defects at the interface due to lattice mismatch is reduced, thereby reducing photoelectric conversion efficiency. Can improve. This can be seen that the XRD peak is shifted according to the composition ratio of Cd x Zn 1-x S in FIG.
도 3은 버퍼층의 물질 및 조성비 변화에 따른 X-선 회절 패턴을 나타낸 그래프이다. 도 3에서, a는 CdS의 버퍼층, b는 Cd0 . 67Zn0 .33S의 버퍼층, c는 Cd0 . 5Zn0 .5S의 버퍼층, d는 Cd0 . 33Zn0 .67S의 버퍼층, e는 ZnS의 버퍼층, f는 Zn(O,S)의 버퍼층을 나타내며, g는 CIGS계 광 흡수층을 나타낸다.3 is a graph showing an X-ray diffraction pattern according to the change of material and composition ratio of the buffer layer. In Figure 3, a is a buffer layer of CdS, b is Cd 0 . 67 a buffer layer of Zn 0 .33 S, c is 0 Cd. 5 Zn buffer of 0 .5 S, d is 0 Cd. 33 a buffer layer of Zn 0 .67 S, e is a buffer layer of ZnS, f denotes a buffer layer of a Zn (O, S), g represents a CIGS-based light absorption layer.
도 3을 참조하면, 버퍼층의 물질 또는 조성비에 따라, X-선 회절(X-ray diffraction, XRD) 패턴이 상이하게 나오는 것을 확인할 수 있으며, 특히, 카드뮴(Cd)과 아연(Zn)의 조성비 변화에 따라, XRD 피크가 쉬프트되는 것을 확인할 수 있다.Referring to FIG. 3, it can be seen that X-ray diffraction (XRD) patterns are different from each other according to the material or composition ratio of the buffer layer. In particular, the composition ratio of cadmium (Cd) and zinc (Zn) changes. As a result, it can be seen that the XRD peak is shifted.
또한, 기존의 CdS 버퍼층(a), ZnS 버퍼층(e), Zn(O,S) 버퍼층(f)에 비하여, CdS와 ZnS를 반복적으로 적층하여 형성한 CdxZn1 - xS 버퍼층(b, c, d)이 CIGS 광 흡수층(g)의 XRD 피크와 유사한 XRD 피크를 갖는 것을 확인할 수 있다. 더욱이, CdxZn1-xS 버퍼층 중에서도 Cd0 . 67Zn0 .33S 버퍼층(b), Cd0 . 5Zn0 .5S 버퍼층(c)의 경우가 CIGS 광 흡수층(g)과 가장 유사한 XRD 피크를 갖는 것을 확인할 수 있다. In addition, compared to the conventional CdS buffer layer (a), ZnS buffer layer (e), and Zn (O, S) buffer layer (f), Cd x Zn 1 - x S buffer layer formed by repeatedly stacking CdS and ZnS (b, It can be seen that c, d) has an XRD peak similar to the XRD peak of the CIGS light absorbing layer (g). Furthermore, among the Cd x Zn 1-x S buffer layers, Cd 0 . 67 Zn 0 .33 S buffer layer (b), Cd 0. For 5 Zn 0 .5 S buffer layer (c) that can be confirmed that the most similar XRD peaks and CIGS light absorption layer (g).
따라서, CdxZn1 - xS의 버퍼층에서, x를 0.5 ~ 0.67의 범위를 갖도록 구성함으로써, 버퍼층의 XRD 피크를 CIGS 광 흡수층의 XRD 피크와 유사하게 형성할 수 있으며, 이를 통해 광전 변환 효율을 향상시킬 수 있다.Therefore, in the buffer layer of Cd x Zn 1 - x S, by configuring x to have a range of 0.5 ~ 0.67, it is possible to form the XRD peak of the buffer layer similar to the XRD peak of the CIGS light absorbing layer, thereby improving the photoelectric conversion efficiency Can be improved.
한편, 태양 전지(100)의 광전 변환 효율은 제1 버퍼층(140)의 두께에 따라 변화될 수 있으며, 예를 들어, 약 10 ~ 20nm의 두께에서 가장 높은 광전 변환 효율을 얻을 수 있다.Meanwhile, the photoelectric conversion efficiency of the solar cell 100 may vary depending on the thickness of the first buffer layer 140. For example, the highest photoelectric conversion efficiency may be obtained at a thickness of about 10 to 20 nm.
제2 버퍼층(150)은 제1 버퍼층(140) 상에 원자층 증착 공정을 통해 형성되며, 산화아연(ZnS)(152)과 황화아연(ZnS)(154)이 교대로 반복적으로 적층되어 형성된다.The second buffer layer 150 is formed through an atomic layer deposition process on the first buffer layer 140, and zinc oxide (ZnS) 152 and zinc sulfide (ZnS) 154 are alternately repeatedly formed. .
제2 버퍼층(150)을 형성함에 있어, 원자층 증착 공정을 이용함으로써 제2 버퍼층(150) 내에 함유된 황(S)과 산소(O)의 조성비를 용이하게 조절할 수 있으며, 황(S)과 산소(O)의 조성비를 조절함으로써 광전 변환 효율을 향상시킬 수 있다. 예를 들어, 제2 버퍼층(150)은 황(S)과 산소(O)의 조성비인 S/(O+S)가 약 10 ~ 25%의 범위로 형성되고, 약 10 ~ 20nm의 두께로 형성될 때 효율상승 효과가 극대화된다. In forming the second buffer layer 150, by using an atomic layer deposition process, the composition ratio of sulfur (S) and oxygen (O) contained in the second buffer layer 150 can be easily adjusted, and sulfur (S) and Photoelectric conversion efficiency can be improved by adjusting the composition ratio of oxygen (O). For example, the second buffer layer 150 is formed of S / (O + S), which is a composition ratio of sulfur (S) and oxygen (O), in a range of about 10 to 25%, and has a thickness of about 10 to 20 nm. When the efficiency increase effect is maximized.
이와 같이, 제1 버퍼층(140)의 형성 후, 제2 버퍼층(150)을 연속적으로 형성함으로써, 이후 형성되는 윈도우층(160) 사이의 격자 부정합을 완화시켜주고, 동시에 생성된 전자가 트랩(trap)될 확률을 감소시켜 광전 변환 효율을 향상시킬 수 있다. 또한, 윈도우층(160)을 구성하는 물질은 주로 ZnO:B 이므로, 동일한 ZnO 계열의 제2 버퍼층(150) 위에 잘 성장되어 격자 부정합에 의해 박리되는 확률을 낮추는 효과를 얻을 수 있다.As described above, after the first buffer layer 140 is formed, the second buffer layer 150 is continuously formed to mitigate lattice mismatch between the window layers 160 formed thereafter, and simultaneously generated electrons trap. The photoelectric conversion efficiency can be improved by reducing the probability of In addition, since the material constituting the window layer 160 is mainly ZnO: B, it is possible to obtain an effect of growing well on the second ZnO-based second buffer layer 150 to lower the probability of peeling due to lattice mismatch.
도 4는 Zn(O,S) 단일 버퍼층을 사용한 태양전지와, CdxZn1 - xS의 제1 버퍼층과 Zn(O,S)의 제2 버퍼층을 같이 사용한 태양전지의 밴드 다이어그램(Band Diagram)을 비교한 도면이다.4 is a band diagram of a solar cell using a Zn (O, S) single buffer layer and a solar cell using a first buffer layer of Cd x Zn 1 - x S and a second buffer layer of Zn (O, S). ).
도 4를 참조하면, Zn(O,S) 단일 버퍼층을 사용할 경우, P-type 광 흡수층과의 밴드 옵셋은 두 증착면의 계면에서 스파이크(spike) 또는 클리프(cliff) 등이 발생하여 전자(electron)나 정공(hole)의 흐름을 방해하는 요소로 작용한다. 반면, CdxZn1 - xS의 제1 버퍼층과 Zn(O,S)의 제2 버퍼층을 같이 사용할 경우, P-type 광 흡수층과의 계면에서 스파이크(spike) 또는 클리프(cliff) 등이 발생되지 않아 전자나 정공의 흐름이 원활해지며, 이에 따라, 상부 전극에서의 전자 수집 확률이 높아져 광전 변환 효율을 향상시킬 수 있다.Referring to FIG. 4, when a Zn (O, S) single buffer layer is used, a band offset with a P-type light absorbing layer may generate spikes or cliffs at an interface between two deposition surfaces, resulting in electrons. ) Or to hinder the flow of holes. On the other hand, when the first buffer layer of Cd x Zn 1 - x S and the second buffer layer of Zn (O, S) are used together, spikes or cliffs occur at the interface with the P-type light absorbing layer. As a result, the flow of electrons and holes is smooth, and thus the probability of electron collection at the upper electrode is increased, thereby improving photoelectric conversion efficiency.
이하, 도 1 및 도 2를 참조하여, 본 발명의 일 실시예에 따른 태양 전지의 제조 방법에 대하여 설명한다.Hereinafter, a method of manufacturing a solar cell according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
도 1을 참조하면, 태양 전지(100)의 제조를 위하여 우선, 기판(110) 상에 전극층(120)을 형성한다. 전극층(120)은 예를 들어, 크롬(Cr), 몰리브덴(Mo), 크롬과 몰리브덴의 합금 등으로 형성할 수 있으며, 물리적 증기 증착법(Physical Vapor Deposition : PVD) 또는 도금 등의 방법으로 형성할 수 있다.Referring to FIG. 1, first, in order to manufacture the solar cell 100, an electrode layer 120 is formed on a substrate 110. The electrode layer 120 may be formed of, for example, chromium (Cr), molybdenum (Mo), an alloy of chromium and molybdenum, or the like, and may be formed by a method such as physical vapor deposition (PVD) or plating. have.
다음으로, 전극층(120) 상에 광 흡수층(130)을 형성한다. 광 흡수층(130)은 구리-인듐-갈륨-셀레나이드(CuInGaSe2, CIGS) 화합물, 구리-인듐-셀레나이드(CuInSe2, CIS) 화합물 또는 구리-아연-틴-황(Cu2ZnSnS4, CZTS) 화합물 등으로 형성될 수 있다. Next, the light absorbing layer 130 is formed on the electrode layer 120. The light absorbing layer 130 may include a copper-indium-gallium-selenide (CuInGaSe 2 , CIGS) compound, a copper-indium-selenide (CuInSe 2 , CIS) compound, or a copper-zinc-tin-sulfur (Cu 2 ZnSnS 4 , CZTS ) Compounds and the like.
광 흡수층(130)은 동시증착법, 스퍼터링법, MOCVD법 등 다양한 방법으로 형성할 수 있다. 이들 중 스퍼터링법을 예를 들면, 구리 타겟, 인듐 타겟 및 갈륨 타겟을 각각 이용하거나, 구리, 인듐 및 갈륨의 혼합 타겟을 이용하여 스퍼터링 방식으로 전극층(120) 상에 구리, 인듐, 가륨(Cu, In, Ga ; CIG) 금속 전구체(precursor)막을 형성한 후, 고온에서 셀레늄(Se)을 이용하여 셀레니제이션(selenization) 공정을 실시함으로써, CIGS 화합물의 광 흡수층(130)을 형성할 수 있다. The light absorbing layer 130 may be formed by various methods such as co-deposition, sputtering, and MOCVD. Among them, a sputtering method using copper, indium and gallium targets, respectively, or using a mixed target of copper, indium and gallium, sputtering on the electrode layer 120 on the electrode layer 120 (Cu, After the In, Ga; CIG) metal precursor (precursor) film is formed, a selenization process may be performed using selenium (Se) at a high temperature to form the light absorbing layer 130 of the CIGS compound.
또한, 광 흡수층(130)은 Ⅰ족 및 Ⅲ족 원소의 적어도 어느 하나로 이루어진 제1 박막층 상에 Ⅵ족 원소로 이루어진 제2 박막층을 형성한 후, 열처리 공정의 실시를 통해 상기 제1 박막층과 상기 제2 박막층을 반응시켜 광 흡수층(130)을 형성할 수 있다. 상기 제1 박막층은 인듐, 구리, 갈륨 박막층으로 형성하거나, 두 원소의 합금과 한 원소의 박막층으로 형성하거나, 세 원소의 합금으로 형성할 수 있고, 상기 제2 박막층은 셀렌 및 황의 적어도 어느 하나로 형성할 수 있다. 즉, 상기 제1 박막층은 Cu/Ga/In, Cu-In 합금/Ga, Cu-Ga 합금/In, Ca-In 합금/Cu, Cu-Ga-In 합금 등으로 이루어질 수 있고, 제2 박막층은 Se, S 또는 Se/S로 이루어질 수 있다. 이와 같이, 상기 제1 박막층 및 상기 제2 박막층은 열처리 공정에 의해 반응시켜 CGS, CIS, CIGS 등의 광 흡수층(130)을 형성할 수 있다. In addition, the light absorbing layer 130 forms a second thin film layer made of a group VI element on the first thin film layer composed of at least one of group I and group III elements, and then performs the heat treatment process to form the first thin film layer and the first layer. The light absorbing layer 130 may be formed by reacting the 2 thin film layers. The first thin film layer may be formed of an indium, copper, gallium thin film layer, an alloy of two elements and a thin film layer of one element, or may be formed of an alloy of three elements, and the second thin film layer is formed of at least one of selenium and sulfur. can do. That is, the first thin film layer may be made of Cu / Ga / In, Cu-In alloy / Ga, Cu-Ga alloy / In, Ca-In alloy / Cu, Cu-Ga-In alloy, and the second thin film layer It may consist of Se, S or Se / S. As such, the first thin film layer and the second thin film layer may be reacted by a heat treatment process to form a light absorbing layer 130 such as CGS, CIS, CIGS, or the like.
구리-아연-틴-황(Cu2ZNSnS4, CZTS) 화합물로 구성된 광 흡수층(130)의 제조공정도 CIGS 광 흡수층의 제조와 매우 유사하며, 주로 구리-아연-틴의 박막 전구체를 스퍼터링법으로 형성하고, 이를 설피제이션(sulfization)하여 CZTS 광 흡수층을 제조할 수 있다.The manufacturing process of the light absorbing layer 130 composed of a copper-zinc-tin-sulfur (Cu 2 ZNSnS 4 , CZTS) compound is also very similar to that of manufacturing a CIGS light absorbing layer, and a thin film precursor of copper-zinc-tin is mainly It may be formed, and sulfation (sulfization) to prepare a CZTS light absorbing layer.
다음으로, 광 흡수층(130) 상에 황화카드뮴(CdS)과 황화아연(ZnS)을 교대로 반복적으로 적층하여 제1 버퍼층(140)을 형성한다. 이후, 제1 버퍼층(140) 상에 산화아연(ZnO)과 황화아연(ZnS)을 교대로 반복적으로 적층하여 제2 버퍼층(150)을 형성한다. 제1 버퍼층(140) 및 제2 버퍼층(150)은 건식 공정이면서 두께나 조성의 조절이 용이한 원자층 증착(Atomic Layer Deposition : ALD) 공정으로 형성된다. Next, cadmium sulfide (CdS) and zinc sulfide (ZnS) are alternately repeatedly stacked on the light absorbing layer 130 to form a first buffer layer 140. Thereafter, zinc oxide (ZnO) and zinc sulfide (ZnS) are alternately repeatedly stacked on the first buffer layer 140 to form a second buffer layer 150. The first buffer layer 140 and the second buffer layer 150 are formed by an atomic layer deposition (ALD) process that is dry and easy to control thickness and composition.
구체적으로, 제1 버퍼층(140)과 제2 버퍼층(150)은 하나의 ALD 장치 내에서 연속적으로 증착하여 형성된다. 예를 들어, 제1 버퍼층(140) 및 제2 버퍼층(150)은 CdS, ZnS, ZnO, ZnS를 반복 증착하기 위해, 디메틸 카드뮴(dimethyl cadmium, DMCd), 디에틸 징크(diethyl zinc, DEZn), H2O, H2S 등을 전구체로 사용할 수 있다. 또한, 퍼지(purge) 가스로는 N2 또는 Ar이 사용되며, 공정 압력은 약 0.1 ~ 2.0torr의 조건에서 형성하는 것이 바람직하다. 또한, 디메틸 카드뮴(DMCd) 및 디에틸 징크(DEZn) 소스를 증발시키기 위한 캐니스터(canister)의 온도는 5 ~ 40℃의 범위를 갖는다.Specifically, the first buffer layer 140 and the second buffer layer 150 are formed by successive deposition in one ALD device. For example, in order to repeatedly deposit CdS, ZnS, ZnO, and ZnS, the first buffer layer 140 and the second buffer layer 150 may be made of dimethyl cadmium (DMCd), diethyl zinc (DEZn), H 2 O, H 2 S and the like can be used as a precursor. In addition, N 2 or Ar is used as the purge gas, and the process pressure is preferably formed at a condition of about 0.1 to 2.0 torr. In addition, the temperature of the canister for evaporating dimethyl cadmium (DMCd) and diethyl zinc (DEZn) sources ranges from 5 to 40 ° C.
제1 버퍼층(140) 및 제2 버퍼층(150)은 황화카드뮴(CdS)(142), 황화아연(ZnS)(144), 산화아연(ZnO) 및 황화아연(ZnS)을 모노레이어(monolayer)로 한 층, 한 층 반복적으로 성막함으로써 조성비를 조절할 수 있다. 예를 들어, 광전 변환 효율의 상승 효과를 극대화시키기 위해, CdxZn1 - xS로 이루어진 제1 버퍼층(140)은 x가 0.5 ~ 0.67의 범위이고, 두께는 10 ~ 20nm로 형성되며, Zn(O,S)로 이루어진 제2 버퍼층(150)은 조성비인 S/(O+S)가 10 ~ 25%의 범위이고, 두께는 10 ~ 20nm로 형성되는 것이 바람직하다.The first buffer layer 140 and the second buffer layer 150 are formed of cadmium sulfide (CdS) 142, zinc sulfide (ZnS) 144, zinc oxide (ZnO), and zinc sulfide (ZnS) as a monolayer. The composition ratio can be adjusted by repeatedly forming one layer and one layer. For example, in order to maximize the synergistic effect of the photoelectric conversion efficiency, the first buffer layer 140 made of Cd x Zn 1 - x S has x in a range of 0.5 to 0.67, a thickness of 10 to 20 nm, and Zn The second buffer layer 150 made of (O, S) has a composition ratio of S / (O + S) of 10 to 25%, and a thickness of 10 to 20 nm.
한편, 제1 버퍼층(140)을 형성함에 있어, 광 흡수층(130)과의 계면특성을 개선하기 위하여, 황화카드뮴(CdS)을 황화아연(ZnS)보다 먼저 증착하는 것이 바람직하다. 이는 광 흡수층(130)의 격자 파라미터(Lattice parameter)와 비교하여 황화아연(ZnS)보다 황화카드뮴(CdS)의 격자 파라미터가 더 유사하기 때문이다. 예를 들어, CIGS의 광 흡수층의 격자 파라미터는 5.8Å이고, 황화카드뮴(CdS)의 격자 파라미터는 5.83Å이며, 황화아연(ZnS)의 격자 파라미터는 5.42Å이다.Meanwhile, in forming the first buffer layer 140, in order to improve the interface characteristics with the light absorbing layer 130, it is preferable to deposit cadmium sulfide (CdS) before zinc sulfide (ZnS). This is because the lattice parameter of cadmium sulfide (CdS) is more similar than that of zinc sulfide (ZnS) compared to the lattice parameter of the light absorbing layer 130. For example, the lattice parameter of the light absorbing layer of CIGS is 5.8 mW, the lattice parameter of cadmium sulfide (CdS) is 5.83 mW, and the lattice parameter of zinc sulfide (ZnS) is 5.42 mW.
원자층 증착(ALD) 방식을 이용한 제1 버퍼층(140) 및 제2 버퍼층(150)의 증착 순서는 소스(DMCd, DEZn) 피딩(feeding) - N2 퍼지 - 소스(H2O, H2S) 피딩 - N2 퍼지의 4단계로 구성되며, 서로 독립 프로세스로 진행된다. 상기한 4단계의 1 사이클을 복수회 반복하여 제1 버퍼층(140) 및 제2 버퍼층(150)을 수십 원자층 두께로 형성할 수 있다. The deposition order of the first buffer layer 140 and the second buffer layer 150 using the atomic layer deposition (ALD) method is source (DMCd, DEZn) feeding-N 2 purge-source (H 2 O, H 2 S ) Feeding-consists of four stages of N 2 purge and are independent processes. The first buffer layer 140 and the second buffer layer 150 may be formed to several tens of atomic layers by repeating the above-described four cycles of the first cycle a plurality of times.
제1 버퍼층(140) 및 제2 버퍼층(150)을 형성함에 있어, 황화카드뮴(CdS)과 황화아연(ZnS), 산화아연(ZnO)의 공정 온도가 서로 상이하므로, 모든 물질의 증착이 가능한 90℃ ~ 130℃의 온도 조건에서 형성하는 것이 바람직하다. 공정 온도가 상기 조건보다 높을 시에는 형성된 모노레이어의 탈착 또는 다음 반응을 위해 표면을 활성화시키는 표면 리간드의 분해, 탈착으로 인해 원하는 품질의 박막을 얻을 수 없을 뿐만 아니라, GPC(growth per cycle)가 낮아지는 문제가 발생되며, 반대로, 공정 온도가 상기 조건보다 낮을 경에도 반응물의 응축이 일어나 박막 특성이 저하되고 GPC가 낮아지는 문제가 발생될 수 있다.In forming the first buffer layer 140 and the second buffer layer 150, the process temperatures of cadmium sulfide (CdS), zinc sulfide (ZnS), and zinc oxide (ZnO) are different from each other. It is preferable to form on the temperature conditions of ° C-130 ° C. When the process temperature is higher than the above conditions, the desorption and desorption of the surface ligand that activates the surface for the next reaction or desorption of the formed monolayer not only results in a thin film of the desired quality, but also has a low growth per cycle (GPC). On the contrary, even when the process temperature is lower than the above conditions, condensation of the reactants may occur, resulting in deterioration of thin film properties and lower GPC.
이와 같이, 혼합 버퍼층(140)을 형성함에 있어, 원자층 증착(ALD) 방법을 통해 모노레이어로 한 층, 한 층 성막함으로써, 박막 내의 결함가 줄어들어 광 반응에 의해 생성된 전자가 버퍼층을 지나면서 트랩(trap)될 확률을 감소시킬 수 있다. 또한, 피딩 및 퍼지 시간과 베포라이즈(vaporize) 제어를 통해 형성하고자 하는 두께를 정확히 제어할 수 있는 장점이 있다. As described above, in forming the mixed buffer layer 140, by depositing one layer and one layer in a monolayer through the atomic layer deposition (ALD) method, defects in the thin film are reduced, and electrons generated by the photoreaction are trapped as they pass through the buffer layer. can reduce the probability of being trapped. In addition, there is an advantage that the thickness to be formed can be precisely controlled through feeding and purge time and vaporization control.
제2 버퍼층(150)의 형성 후, 제2 버퍼층(150) 상에 투명 도전성 물질로 이루어진 윈도우층(160)을 형성한다. 윈도우층(160)은 예를 들어, 산화아연(ZnO)에 알루미늄(Al) 또는 붕소(B)가 도핑되어 형성될 수 있다. After the formation of the second buffer layer 150, a window layer 160 made of a transparent conductive material is formed on the second buffer layer 150. The window layer 160 may be formed by, for example, doping aluminum (Al) or boron (B) with zinc oxide (ZnO).
윈도우층(160)은 유기금속화학증착(MOCVD) 공정 또는 스퍼터링 공정을 통해 형성할 수 있다. 예를 들어, 윈도우층(160)은 아연(Zn) 소오스, 산소(O2) 소오스, 및 도펀트 가스(예를 들어, B2H6)를 동시에 공급하여 유기금속화학증착(MOCVD) 공정으로 ZnO:B층을 형성할 수 있다. 또한, 윈도우층(160)은 ZnO:Al2O3을 타겟으로 한 스퍼터링 공정으로 ZnO:Al층으로 형성할 수 있고, 알곤(Ar)+산소(O2) 분위기에서 Zn:Al 타겟을 이용하여 ZnO:Al층을 형성할 수도 있다. The window layer 160 may be formed through an organometallic chemical vapor deposition (MOCVD) process or a sputtering process. For example, the window layer 160 supplies a zinc (Zn) source, an oxygen (O 2 ) source, and a dopant gas (for example, B 2 H 6 ) at the same time to ZnO in an organometallic chemical vapor deposition (MOCVD) process. A B layer can be formed. In addition, the window layer 160 may be formed of a ZnO: Al layer by a sputtering process targeting ZnO: Al 2 O 3 and using a Zn: Al target in an argon (Ar) + oxygen (O 2 ) atmosphere. A ZnO: Al layer can also be formed.
도 5는 본 발명에 따른 제1 및 제2 버퍼층과 기존의 카드뮴 버퍼층을 사용한 경우의 모듈 효율을 비교한 그래프이다.5 is a graph comparing module efficiency when the first and second buffer layers and the conventional cadmium buffer layer according to the present invention are used.
도 5를 참조하면, 본 발명의 실시예와 같이 CdxZn1 - xS의 제1 버퍼층(140)과 Zn(O,S)의 제2 버퍼층(150)으로 이루어진 더블 버퍼층 구조를 사용하는 경우, 기존의 황화카드뮴(CdS)을 버퍼층으로 사용하는 경우에 비해, 모듈 효율이 향상되는 것을 확인할 수 있다.Referring to FIG. 5, when the double buffer layer structure including the first buffer layer 140 of Cd x Zn 1 - x S and the second buffer layer 150 of Zn (O, S) is used as in the exemplary embodiment of the present invention. As compared with the case of using the conventional cadmium sulfide (CdS) as the buffer layer, it can be seen that the module efficiency is improved.
앞서 설명한 본 발명의 상세한 설명에서는 본 발명의 바람직한 실시예들을 참조하여 설명하였지만, 해당 기술분야의 숙련된 당업자 또는 해당 기술분야에 통상의 지식을 갖는 자라면 후술될 특허청구범위에 기재된 본 발명의 사상 및 기술 영역으로부터 벗어나지 않는 범위 내에서 본 발명을 다양하게 수정 및 변경시킬 수 있음을 이해할 수 있을 것이다.In the detailed description of the present invention described above with reference to the preferred embodiments of the present invention, those skilled in the art or those skilled in the art having ordinary skill in the art will be described in the claims to be described later It will be understood that various modifications and variations can be made in the present invention without departing from the scope of the present invention.

Claims (12)

  1. 기판 상에 형성된 전극층;An electrode layer formed on the substrate;
    상기 전극층 상에 형성된 광 흡수층;A light absorbing layer formed on the electrode layer;
    상기 광 흡수층 상에 원자층 증착(ALD) 공정을 통해 형성되며, 황화카드뮴(CdS)과 황화아연(ZnS)이 교대로 반복적으로 적층되어 형성된 제1 버퍼층; A first buffer layer formed on the light absorbing layer through an atomic layer deposition (ALD) process, wherein cadmium sulfide (CdS) and zinc sulfide (ZnS) are alternately repeatedly stacked;
    상기 제1 버퍼층 상에 원자층 증착 공정을 통해 형성되며, 산화아연(ZnO)과 황화아연(ZnS)이 교대로 반복적으로 적층되어 형성된 제2 버퍼층; 및A second buffer layer formed on the first buffer layer through an atomic layer deposition process and formed by alternately repeatedly depositing zinc oxide (ZnO) and zinc sulfide (ZnS); And
    상기 제2 버퍼층 상에 형성된 윈도우층을 포함하는 태양 전지.The solar cell comprising a window layer formed on the second buffer layer.
  2. 제1항에 있어서, The method of claim 1,
    상기 제1 버퍼층은 CdxZn1 - xS이며, 상기 x는 0.5 ~ 0.67로 구성되는 것을 특징으로 하는 태양 전지.The first buffer layer is Cd x Zn 1 - x S, wherein x is composed of 0.5 ~ 0.67 solar cell.
  3. 제1항에 있어서, The method of claim 1,
    상기 제1 버퍼층은 10 ~ 20nm의 두께로 형성되는 것을 특징으로 하는 태양 전지.The first buffer layer is a solar cell, characterized in that formed in a thickness of 10 ~ 20nm.
  4. 제1항에 있어서, The method of claim 1,
    상기 제2 버퍼층은 황(S)과 산소(O)의 조성비인 S/(O+S)가 10 ~ 25%의 범위로 구성되는 것을 특징으로 하는 태양 전지.The second buffer layer is a solar cell, characterized in that the composition ratio of sulfur (S) and oxygen (O) S / (O + S) in the range of 10 to 25%.
  5. 제1항에 있어서, The method of claim 1,
    상기 제2 버퍼층은 10 ~ 20nm의 두께로 형성되는 것을 특징으로 하는 태양 전지.The second buffer layer is a solar cell, characterized in that formed in a thickness of 10 ~ 20nm.
  6. 기판 상에 전극층을 형성하는 단계;Forming an electrode layer on the substrate;
    상기 전극층 상에 광 흡수층을 형성하는 단계;Forming a light absorbing layer on the electrode layer;
    상기 광 흡수층 상에 원자층 증착(ALD) 공정을 통해 황화카드뮴(CdS)과 황화아연(ZnS)을 교대로 반복적으로 적층하여 제1 버퍼층을 형성하는 단계; Alternately repeatedly forming cadmium sulfide (CdS) and zinc sulfide (ZnS) on the light absorbing layer through an atomic layer deposition (ALD) process to form a first buffer layer;
    상기 제1 버퍼층 상에 원자층 증착 공정을 통해 산화아연(ZnO)과 황화아연(ZnS)을 교대로 반복적으로 적층하여 제2 버퍼층을 형성하는 단계; 및Forming a second buffer layer by alternately repeatedly depositing zinc oxide (ZnO) and zinc sulfide (ZnS) on the first buffer layer through an atomic layer deposition process; And
    상기 제2 버퍼층 상에 윈도우층을 형성하는 단계를 포함하는 태양 전지의 제조 방법.Forming a window layer on the second buffer layer.
  7. 제6항에 있어서, The method of claim 6,
    상기 제1 버퍼층은 CdxZn1 - xS이며, 상기 x는 0.5 ~ 0.67로 구성되는 것을 특징으로 하는 태양 전지의 제조 방법.The first buffer layer is Cd x Zn 1 - x S, wherein x is a method of manufacturing a solar cell, characterized in that consisting of 0.5 ~ 0.67.
  8. 제6항에 있어서, The method of claim 6,
    상기 제1 버퍼층은 10 ~ 20nm의 두께로 형성되는 것을 특징으로 하는 태양 전지의 제조 방법.The first buffer layer is a manufacturing method of a solar cell, characterized in that formed in a thickness of 10 ~ 20nm.
  9. 제6항에 있어서, The method of claim 6,
    상기 제1 버퍼층을 형성함에 있어, 황화카드뮴을 황화아연보다 먼저 증착하는 것을 특징으로 하는 태양 전지의 제조 방법.In forming the first buffer layer, cadmium sulfide is deposited prior to zinc sulfide.
  10. 제6항에 있어서, The method of claim 6,
    상기 제2 버퍼층은 황(S)과 산소(O)의 조성비인 S/(O+S)가 10 ~ 25%의 범위로 구성되는 것을 특징으로 하는 태양 전지의 제조 방법.The second buffer layer is a manufacturing method of a solar cell, characterized in that the composition ratio of sulfur (S) and oxygen (O) S / (O + S) in the range of 10 to 25%.
  11. 제6항에 있어서, The method of claim 6,
    상기 제2 버퍼층은 10 ~ 20nm의 두께로 형성되는 것을 특징으로 하는 태양 전지의 제조 방법.The second buffer layer is a method of manufacturing a solar cell, characterized in that formed in a thickness of 10 ~ 20nm.
  12. 제6항에 있어서, The method of claim 6,
    상기 제1 버퍼층 및 제2 버퍼층은 90℃ ~ 130℃의 온도 조건에서 형성되는 것을 특징으로 하는 태양전지의 제조 방법.The first buffer layer and the second buffer layer is a manufacturing method of a solar cell, characterized in that formed at a temperature condition of 90 ℃ ~ 130 ℃.
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