WO2008105597A1

WO2008105597A1 - Transparent electrode for solar cell and manufacturing method thereof

Info

Publication number: WO2008105597A1
Application number: PCT/KR2008/001007
Authority: WO
Inventors: Chong-Chan Lee; Jong-Bok Kim; Ho-Gi Bae
Original assignee: Dongjin Semichem Co Ltd
Current assignee: Dongjin Semichem Co Ltd
Priority date: 2007-02-28
Filing date: 2008-02-21
Publication date: 2008-09-04
Anticipated expiration: 2009-08-28
Also published as: KR101352779B1; TW200840061A; CN101622721B; TWI456772B; CN101622721A; KR20080079891A

Abstract

The present invention relates to a transparent electrode for a solar cell and a manufacturing method thereof, and more particularly to a transparent electrode which is transparent and conductive to be employed in a solar cell, the transparent electrode comprising a transparent base layer; a first polycrystalline transparent metal oxide layer which is formed on the transparent base layer; a metal layer which is formed on the first polycrystalline transparent metal oxide layer; and a second polycrystalline transparent metal oxide layer formed on the metal layer, and a manufacturing method thereof. Thus, the transparent electrode according to the present invention minimizes a lowering of light transmittance, sharply reduces specific resistance and improves a surface roughness to thereby enhance efficiency of a solar cell and provide a high-efficiency solar cell.

Description

TRANSPARENT ELECTRODE FOR SOLAR CELL AND MANUFACTURING METHOD THEREOF

Technical Field

[1] The present invention relates to a transparent electrode for a solar cell and a manufacturing method thereof, and more particularly, to a high quality transparent electrode for a solar cell which minimizes a lowering of light transmittance, sharply reduces specific resistance and improves a surface roughness to thereby enhance efficiency of a solar cell and provide a high efficiency solar cell, and a manufacturing method thereof. Background Art

[2] A conductive, transparent electrode is widely employed for various technical applications and also required to be developed for various areas, and particularly, for areas such as solar cells and display elements. As disclosed in Korean Patent Application No. 2006-0053541, a transparent electrode which provides high conductivity and light transmittance rate is mainly used in a solar cell producing electricity with sunlight and in a display element displaying a light signal generated from a substrate to the outside. To that end, the transparent electrode is manufactured by depositing a conductive material such as ITO (indium tin oxide) on an insulating base layer such as glass by sputtering. Particularly, a transparent electrode which is employed in an OLED (organic light emitting diode) requires a conductive material layer to have lower specific resistance and higher planarization because of characteristics of the OLED. Here, higher planarization is more necessary than lower specific resistance since the OLED layer is thin. As for a transparent electrode employed in a solar cell, however, photoelectric conversion efficiency is most critical. Thus, it is essential that the conductive material has low specific resistance together with high light transmittance because of the characteristics of the application area.

[3] To develop a high-efficiency solar cell, a conductive material layer which is deposited on a transparent base layer should have lower specific resistance and lower surface roughness while providing higher transmittance. However, a conventional amorphous ITO has a high specific resistance while having high planarization. Meanwhile, polycrystalline ITO has a lower specific resistance than the amorphous ITO does, but still higher. Also, a surface of the polycrystalline ITO is very rough.

[4] Thus, it is highly required to develop a manufacturing method of a transparent electrode which maintains transmittance similarly to that of a conventional transparent electrode, sharply reduces specific resistance and improves surface roughness while using a newly-developed metal oxide disclosed in Korean Patent Application No. 2006-0053541 or an existing metal oxide and utilizing existing deposition equipment. Disclosure of Invention

Technical Problem

[5] Accordingly, it is an aspect of the present invention to provide a high quality transparent electrode for a solar cell which minimizes a lowering of transmittance, sharply reduces specific resistance and improves a surface roughness to thereby enhance efficiency of a solar cell and provide a high efficiency solar cell, and a manufacturing method thereof.

[6] Additional aspects and/or advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present invention. Technical Solution

[7] The foregoing and/or other aspects of the present invention are achieved by providing a transparent electrode which is transparent and conductive to be employed in a solar cell, the transparent electrode comprising a transparent base layer; a first polycrystalline transparent metal oxide layer which is formed on the transparent base layer; a metal layer which is formed on the first polycrystalline transparent metal oxide layer; and a second polycrystalline transparent metal oxide layer which is formed on the metal layer.

[8] The foregoing and/or other aspects of the present invention are also achieved by providing a solar cell which comprises the transparent electrode for the solar cell, and a counter electrode facing the transparent electrode.

[9] The foregoing and/or other aspects of the present invention are also achieved by providing a manufacturing method of a transparent electrode for a solar cell, the manufacturing method comprising providing a transparent base layer; forming a first polycrystalline transparent metal oxide layer on the transparent base layer; forming a metal layer on the first polycrystalline transparent metal oxide layer; and forming a second polycrystalline transparent metal oxide layer on the metal layer.

Advantageous Effects

[10] As described above, the present invention provides a transparent electrode for a solar cell, a solar cell including the same and a manufacturing method thereof which minimizes a lowering of light transmittance, sharply reduces specific resistance and improves a surface roughness to thereby enhance efficiency of a solar cell and provide a high-efficiency solar cell. Brief Description of the Drawings

[11] The above and/or other aspects of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

[12] FIG. 1 is a sectional view of a transparent electrode according to an exemplary embodiment of the present invention;

[13] FIG. 2 is a sectional view of a dye- sensitized solar cell which employs the transparent electrode according to the present invention;

[14] FIG. 3 is a surface of the transparent electrode for the solar cell according to the present invention, captured by a scanning microscope; and

[15] FIG. 4 is a surface of a transparent electrode according to a comparative embodiment, captured by a scanning microscope. Mode for the Invention

[16] Hereinafter, exemplary embodiments of the present invention will be described with reference to accompanying drawings, wherein like numerals refer to like elements and repetitive descriptions will be avoided as necessary.

[17] Hereinafter, the present invention will be described in detail.

[18] The present invention relates to a transparent electrode for a solar cell which is transparent and conductive. The transparent electrode includes a transparent base layer 10, a first poly crystalline transparent metal oxide layer 20 formed on the transparent base layer 10, a metal layer 30 formed on the first poly crystalline transparent metal oxide layer 20 and a second polycrystalline transparent metal oxide layer 40 formed on the metal layer 30.

[19] Generally, a solar cell includes a transparent electrode through which sunlight is incident, and a counter electrode which faces the transparent electrode. The transparent electrode should be both transparent and conductive to flow electricity therein. Thus, the transparent electrode is manufactured by a conductive material. If the transparent electrode material includes an insulating material, a conductive material is coated on the insulating material. According to the present invention, as shown in FIG. 1, the transparent electrode includes the transparent base layer 10, the first polycrystalline transparent metal oxide layer 20 formed on the transparent base layer 10, the metal layer 30 formed on the first polycrystalline transparent metal oxide layer 20 and the second polycrystalline transparent metal oxide layer 40 formed on the metal layer 30. According to the present invention, electrical conductivity of the conductive material layer is maximized by using a metal having a lower specific resistance. As oxide layers 20 and 40 are formed on and under the metal layer 30 to reflect metal reflective light again, i.e., the metal layer 30 is sandwiched between the oxide layers 20 and 40 to minimize the lowering of transmittance due to the introduction of the metal layer 30, highly-electrical conductive multiple layers may be manufactured.

[20] The transparent base layer 10 may include various known transparent materials to be employed in a solar cell, e.g., an insulating body or a conductive body. Preferably, the transparent base layer 10 includes glass which has structural and chemical stability.

[21] The oxide layer 20 is formed on the transparent base layer 10 to apply high conductivity to the transparent base layer 10, to provide a surface to form the metal layer 30 thereon and to prevent the metal layer 30 from being introduced thereto. The oxide layer 20 forms the first polycrystalline transparent metal oxide layer 20 including crystalloid rather than amorphous. The transparent metal oxide may include various known metal oxides which are transparent and conductive. More specifically, the transparent metal oxide may include e.g., tin oxide having antimony or fluorine as a dopant, zinc oxide having aluminium or potassium as a dopant, ITO having tin as a dopant or crystal In-W-O of Japanese Patent First Publication No. 2004-43851. Preferably, the transparent metal oxide may include ITO or FTO which is widely used, convenient and highly-conductive, and more preferably, ITO. That is, the transparent metal oxide layer (film) which acts as an antireflection layer due to the introduction of the metal layer 30 includes ITO widely used for an existing transparent conductive layer. The ITO layer provides high transmittance in the visible ray area while having a low specific resistance. Also, the ITO layer has good surface planarization and highly refractive index by controlling the deposition condition. Thus, when the metal layer is 30 formed later, it is not broken, but continuous even if it is thin. Further, the specific resistance is lowered. Thus, the ITO layer is appropriate for the antireflection layer of the metal layer 30.

[22] Further, the first polycrystalline transparent metal oxide layer 20 influences on optical activity to enhance transmittance rate, prevents diffusion of a substrate material and acts as a nucleation modification layer influencing on initial nuclei generation of metal, as well as playing a critical role in determining planarization of the overall sandwich configuration.

[23] The ITO transparent metal oxide layer may be formed by various known deposition methods, e.g., vacuum deposition, ion plating, sputtering, a method of applying a liquid to form a transparent conductive layer, etc. The ITO transparent metal oxide layer is preferably formed by sputtering to control the thickness and for conveniences. In this case, the ITO transparent metal oxide layer should include polycrystalline to lower the specific resistance and to prevent diffusion and coupling of the metal layer 30 and the oxide layers 20 and 40. Generally, amorphous ITO is annealed into polycrystalline. Preferably, the thickness of the first polycrystalline transparent metal oxide layer 20 ranges from 250 to 800 A to secure sufficient transmittance and to improve conductivity by forming the metal layer 30 within a range not damaging the transmittance. In this case, the surface roughness does not deteriorate. As the polycrystalline ITO has anisotropy having a rapid crystal growth rate in the direction (400), the surface roughness deteriorates and the transmittance is lowered or the metal layer 30 becomes thicker if polycrystalline grows too much. Thus, the thickness of the first polycrystalline transparent metal oxide layer 20 is preferably within the foregoing range. [24] As shown in FIG. 1, the metal layer 30 is formed on the first polycrystalline transparent metal oxide layer 20. As a specific resistance of the conductive material of the transparent base layer 10 is sharply reduced by the metal layer 30, a thicker metal layer is better in an aspect of electrical conductivity. However, if the metal layer 30 is too thick, the transmittance of the transparent electrode is lowered. Thus, the thickness of the metal layer 30 is preferably a maximum of 500 A more preferably 50 to 150 A and most preferably around 100 A to secure sufficient conductivity and transmittance. After all, most of electrical conductivity is implemented by the metal layer 30, and thus the metal layer 30 should be planar, complete and continuous.

[25] The metal layer 30 may include various known metals which are highly conductive.

Preferably, the metal layer 30 includes a material that is selected at least one from the group consisting of silver (Ag), silver alloy, platinum (Pt), platinum ally, gold (Au), gold alloy, copper (Cu), copper alloy and a mixture (alloy) thereof which is highly conductive and easily deposited. More preferably, the metal layer 30 includes a material that is selected at least one from the group consisting of silver (Ag), platinum (Pt), gold (Au), copper (Cu) and a mixture (alloy) thereof, and most preferably silver (Ag) which is highly conductive. If the metal layer 30 includes silver that is highly conductive and absorbs less visible rays, the transparent electrode for the solar cell has sufficient transmittance rate with multiple layers.

[26] The metal layer 30 may be formed by various known deposition methods, and preferably by sputtering to be manufactured without difficulty and to adjust the thickness. Preferably, the metal layer 30 is formed by room temperature deposition process without heating the base layer to restrain the coarsening of the first polycrystalline metal oxide layer 20 and interaction between the metal and metal oxide and to lower the specific resistance.

[27] As the metal layer 30 is thin and may act as a chemical impurity, the second polycrystalline transparent metal oxide layer 40 may be further formed on the metal layer 30 by the same method as that of the first polycrystalline transparent metal oxide layer 20 to thereby protect and contain the metal layer 30. The second polycrystalline transparent metal oxide layer 40 acts as an antireflection layer optically and enhances transmittance rate as well as protecting the metal layer 30.

[28] The second polycrystalline transparent metal oxide layer 40 may include polycrystalline to improve electrical conductivity. The second polycrystalline transparent metal oxide layer 40 is required to have a planar surface to form other layers later without difficulty and to secure transmittance. Preferably, the thickness of the second polycrystalline transparent metal oxide layer 40 ranges from 250 to 800 A not to lower the surface roughness and to secure the transmittance.

[29] Also, the present invention provides a solar cell which includes the transparent electrode according to the present invention. The solar cell includes the transparent electrode for the solar cell, and a counter electrode facing the transparent electrode. The solar cell includes various known solar cells having a transparent electrode to which sunlight is incident. For example, the solar cell includes a silicon type solar cell, a dye-sensitized solar cell and the like. The configuration of the foregoing solar cells is known in the art, and thus detailed descriptions will be omitted.

[30] FIG. 2 illustrates a dye-sensitized solar cell which includes the transparent electrode according to the present invention. As shown therein, the solar cell includes the transparent electrode having i) the transparent base layer 10, ii) the conductive layer (20+30+40) including the first polycrystalline transparent metal oxide layer 20, the metal layer 30 and the second polycrystalline transparent metal oxide layer 40, and the counter electrode (70+80+90) (a catalyst metal layer 70 including platinum, a conductive coating layer 80 and a glass layer 90 as a base of the counter electrode). Meanwhile, a dye-sensitized solar cell may further include a porous layer 50 including a dye and an electrolyte layer 60 formed on the porous layer 50.

[31] Further, the present invention provides a manufacturing method of the transparent electrode for a solar cell. The manufacturing method of the transparent electrode for the solar cell according to the present invention includes an operation of providing a transparent base layer, an operation of forming the first polycrystalline transparent metal oxide layer on the transparent base layer, an operation of forming the metal layer on the first polycrystalline transparent metal oxide layer and an operation of forming the second polycrystalline transparent metal oxide layer on the metal layer.

[32] The material of the transparent base layer 10, the transparent metal oxide layers 20 and 40 and the metal layer 30 is described as above. Preferably, the transparent metal oxide layers 20 and 40 include ITO and the metal layer 30 includes silver (Ag). The metal layer 30 may be formed while the base layer 10 is at room temperatures, to thereby lower the specific resistance and manufacture high efficiency solar cell. The ITO layer may be formed by annealing amorphous ITO into polycrystalline. More preferably, the ITO layer is formed while the base layer 10 has heat of 200 + 50 ⁰C. Under such circumstances, the ITO layer is manufactured without difficulty, grows properly and secures appropriate roughness.

[33] The method of forming the transparent metal oxide layers 20 and 40 and the metal layer 30 may include various known methods, and preferably a sputtering vacuum deposition method as described above. [34] Preferably, the thickness of the metal layer 30 is a maximum of 500 A, and more preferably 50 to 150 A. The thickness of the first poly crystalline transparent metal oxide layer 20 is 250 to 800 A and that of the second polycrystalline transparent metal oxide layer 40 is 250 to 800 A.

[35] To further reduce the specific resistance corresponding to the polycrystalline metal oxide layers 20 and 40, the overall transparent electrode is preferably annealed after the foregoing manufacturing process. Thus, the resistance at a grain boundary may be lowered and the specific resistance may be reduced. The annealing condition may include known annealing conditions. The ITO metal oxide is heat treated at 220 ± 50 0C for 30 minutes to 2 hours to restrain the coarsening of the particle size and surface reaction and to lower the specific resistance.

[36] Hereinafter, exemplary embodiments of the present invention and a comparative embodiment will be described. The embodiments exemplify the present invention, but do not confine the scope of the present invention.

[37] [Exemplary embodiment]

[38] Exemplary embodiments 1 and 2 and Comparative embodiment 1

[39] A sample was prepared on a glass base with the configuration of layers (p-ITO refers to polycrystalline ITO), thickness condition, deposition temperature condition and annealing treatment condition as shown in Table 1. As shown in Table 1, a silver (Ag) layer was deposited at room temperatures. After the sample was provided, surface resistance, specific resistance, (light) transmittance and surface roughness were measured and shown in Table 2.

[40]

[41] Table 1

[Table 1] [Table ]

[42] [43] As shown in Table 2, the transparent electrodes according to the exemplary embodiments 1 and 2 have much lower surface resistance and specific resistance and improve electrical conductivity more than that according to the comparative embodiment. Also, the transparent electrodes according to the exemplary embodiments 1 and 2 rarely lose transmittance, and improve surface roughness. As shown in FIG. 3, the transparent electrode according to the exemplary embodiment 1 has a minute configuration in which crystal grains are not coarsened while the transparent electrode according to the comparative embodiment has larger crystal grains and a higher roughness value.

[44] [45] Table 2

[Table 2] [Table ]

[46] [47] Although a few exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents. Industrial Applicability

[48] As described above, the present invention provides a transparent electrode for a solar cell, a solar cell including the same and a manufacturing method thereof which minimizes a lowering of light transmittance, sharply reduces specific resistance and improves a surface roughness to thereby enhance efficiency of a solar cell and provide a high-efficiency solar cell.

Claims

[1] A transparent electrode which is transparent and conductive to be employed in a solar cell, the transparent electrode, comprising: a transparent base layer; a first polycrystalline transparent metal oxide layer which is formed on the transparent base layer; a metal layer which is formed on the first polycrystalline transparent metal oxide layer; and a second polycrystalline transparent metal oxide layer which is formed on the metal layer.

[2] The transparent electrode according to claim 1, wherein the metal layer is selected at least one from a group consisting of silver (Ag), platinum (Pt), gold

(Au), copper (Cu) and a mixture(alloy) thereof, and the transparent metal oxide layer comprises indium tin oxide (ITO) or fluorine tin oxide (FTO).

[3] The transparent electrode according to claim 1, wherein a thickness of the metal layer is a maximum of 500 A.

[4] The transparent electrode according to claim 3, wherein a thickness of the first polycrystalline transparent metal oxide layer ranges from 250 to 800 A a thickness of the metal layer ranges from 50 to 150 A and a thickness of the second polycrystalline transparent metal oxide layer is 250 to 800 A.

[5] The transparent electrode according to claim 1, wherein the metal layer is manufactured by a room temperature deposition process.

[6] A solar cell which comprises a transparent electrode for a solar cell according to one of claims 1 to 5, and a counter electrode facing the transparent electrode.

[7] The solar cell according to claim 6, further comprising a porous layer having a dye and an electrolyte layer which are disposed between the transparent electrode and the counter electrode.

[8] A manufacturing method of a transparent electrode for a solar cell, the manufacturing method comprising: providing a transparent base layer; forming a first polycrystalline transparent metal oxide layer on the transparent base layer; forming a metal layer on the first polycrystalline transparent metal oxide layer; and forming a second polycrystalline transparent metal oxide layer on the metal layer.

[9] The manufacturing method according to claim 8, further comprising annealing the transparent electrode for the solar cell after the foregoing operations.

[10] The manufacturing method according to claim 9, wherein the transparent metal oxide comprises indium tin oxide (ITO), and the annealing the transparent electrode comprises heat-treating the transparent electrode at 220 ± 50 ⁰C for 30 minutes to two hours.

[11] The manufacturing method according to claim 8 or 9, wherein the transparent metal oxide layer and the metal layer are formed by a sputtering vacuum deposition method.

[12] The manufacturing method according to claim 8 or 9, wherein the transparent metal oxide comprises ITO, and the metal layer comprises silver (Ag) and formed when the base layer is at room temperatures.

[13] The manufacturing method according to claim 12, wherein the ITO layer is formed when the base layer has a heat of 200 ± 50 ⁰C.

[14] The manufacturing method according to claim 8 or 9, wherein a thickness of the first polycrystalline transparent metal oxide layer ranges from 250 to 800 A a thickness of the metal layer ranges from 50 to 150 A and a thickness of the second polycrystalline transparent metal oxide layer is 250 to 800 A.