Patent Publication Number: US-2012024367-A1

Title: Electrode for photoelectric conversion device, method of preparing the same and photoelectric conversion device comprising the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0073443, filed on Jul. 29, 2010, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects of embodiments of the present invention relate to an electrode for a photoelectric conversion device, a method of preparing the same and a photoelectric conversion device comprising the same. 
     2. Description of the Related Art 
     A solar cell is a desired energy source because solar energy is virtually unlimited and eco-friendly unlike other energy sources. Solar cells can be classified into silicon solar cells, dye solar cells, etc. 
     Silicon solar cells are difficult to be put to practical use because their fabrication costs are relatively high. Further, it is very difficult to improve the efficiency of the silicon solar cells. 
     On the other hand, dye solar cells are photoelectric chemical solar cells using a dye molecule and a transition metal oxide as main materials. Here, the dye molecule generates electron-hole pairs by absorbing visible light, and the transition metal oxide transfers the generated electrons. Since the dye solar cells have remarkably lower fabrication costs than existing silicon-based solar cells, it is possible to substitute them for existing amorphous silicon solar cells. 
     A metal electrode layer of the dye solar cell is formed to protrude from a transparent electrode on a substrate, and a protection layer for preventing (or protecting from) corrosion of the metal electrode layer is formed on a protruded portion of the metal electrode layer that is in a region which is filled with an electrolyte solution and sealed by a sealing material. 
     If the metal electrode layer is protruded from the substrate as described above, a difference in interfaces between regions occurs. In one region, the protruded metal electrode layer is formed, and the protection layer is also formed on the metal electrode layer. In another region, only the protruded metal electrode layer is formed, and the protection layer is not formed. Here, the protection layer is not formed on the lower surface of the sealing material, and the electrolyte solution may leak due to the decrease of adhesion of the sealing material or the looseness of the sealing material due to the protruded metal electrode layer itself. Therefore, there is a problem in view of the reliability of products. 
     SUMMARY 
     An aspect of an embodiment of the present invention is directed toward an electrode for a photoelectric conversion device, a method of preparing the same and a photoelectric conversion device comprising the same, which can enhance the reliability of products by improving or enhancing the shape of a protruded electrode. 
     According to an embodiment of the present invention, there is provided an electrode for a photoelectric conversion device, the electrode including: a transparent conductive layer formed on a substrate to have spacing regions formed at a set interval; a metal electrode layer formed in a corresponding one of the spacing regions; and a protection layer formed on the transparent conductive layer and the metal electrode layer to coat the metal electrode layer. 
     The substrate may have groove portions with a set pattern. 
     The positions of the groove portions may match the respective spacing regions. 
     The metal electrode layer may have a shape matching a corresponding one of the groove portions. 
     The cross-section of each of the groove portions in the thickness direction of the substrate may have a polygonal shape, a polygonal cone shape, an elliptic shape, or a circular shape. 
     A lower surface of the metal electrode layer may contact an upper surface of the substrate. 
     The height of an upper surface of the metal electrode layer may be between the height of the upper surface of the substrate and the height of an upper surface of the transparent conductive layer. 
     The protection layer may have a thickness at or between 10 and 50 μm. 
     According to an embodiment of the present invention, there is provided a method of preparing an electrode for a photoelectric conversion device, the method including: providing a substrate having a transparent conductive layer formed thereon; patterning the transparent conductive layer to have spacing regions formed at a set interval; forming a metal electrode layer in a corresponding one of the spacing regions; and forming a protection layer on the transparent conductive layer and the metal electrode layer to coat the metal electrode layer. 
     The method may further include forming groove portions with a set pattern on the substrate before the forming of the metal electrode layer. 
     The positions of the groove portions may match the respective spacing regions. 
     The metal electrode layer may have a shape matching a corresponding one of the groove portions. 
     The cross-section of each of the groove portions in the thickness direction of the substrate may have a polygonal shape, a polygonal cone shape, an elliptic shape, or a circular shape. 
     In the forming of the metal electrode layer, a lower surface of the metal electrode layer may come in contact with an upper surface of the substrate. 
     In the forming of the metal electrode layer, the height of an upper surface of the metal electrode layer may be between the height of the upper surface of the substrate and the height of an upper surface of the transparent conductive layer. 
     In the forming of the protection layer, the protection layer may have a thickness at or between 10 and 50 μm. 
     According to an embodiment of the present invention, there is provided a photoelectric conversion device including: a first substrate; a first electrode on the first substrate; a photoelectrode layer on at least one surface of the first electrode, the photoelectrode layer including a photo-sensitizing dye; a second substrate; a second electrode on the second substrate and facing the first electrode; a counter-electrode layer on at least one surface of the second electrode, the counter-electrode layer including a conductive catalyst; a sealing member joining the first and second electrodes; and an electrolyte solution injected into a space between the first and second electrodes and sealed in the space between the first and second electrodes by the sealing member, wherein at least one of the first and second electrodes includes a transparent conductive layer formed on a corresponding one of the first and second substrates and having a plurality of spacing regions at a set interval, a metal electrode layer formed in a corresponding one of the spacing regions, and a protection layer formed on the transparent conductive layer and the metal electrode layer to coat the metal electrode layer. 
     As described above, according to the embodiments of the present invention, the shape of a protruded electrode is improved, so that the reliability of products can be enhanced through a simple process. 
     Also, as the metal electrode layer has a structure in which the step difference is reduced as described above, the leakage of the electrolyte solution due to the degradation of the adhesion of the sealing member or the looseness of the sealing member can be reduced, thereby enhancing the reliability of products. 
     Also, while three surfaces of the metal electrode layer were conventionally exposed, only the upper surface of the metal electrode layer is now exposed. Thus, it is possible to decrease the possibility of corrosion of the metal electrode layer, which may be caused by the crack or looseness of the protection layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention. 
         FIG. 1  is a sectional view schematically showing the entire configuration of a photoelectric conversion device according to an embodiment of the present invention. 
         FIG. 2  is a view schematically showing the state in which a dye is connected to an inorganic metal oxide semiconductor. 
         FIG. 3  is a plan view schematically showing a partial configuration of the photoelectric conversion device. 
         FIG. 4  is a sectional view schematically showing the structure of an electrode for the photoelectric conversion device according to a first embodiment of the present invention. 
         FIG. 5  is a sectional view schematically showing the structure of an electrode for the photoelectric conversion device according to a second embodiment of the present invention. 
         FIG. 6  is a sectional view schematically showing the structure of an electrode for the photoelectric conversion device according to a third embodiment of the present invention. 
         FIG. 7  is a sectional view schematically showing the structure of an electrode for the photoelectric conversion device according to a fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. In addition, when an element is referred to as being “on” another element, it can be directly on the another element or be indirectly on the another element with one or more intervening elements interposed therebetween. Also, when an element is referred to as being “connected to” another element, it can be directly connected to the another element or be indirectly connected to the another element with one or more intervening elements interposed therebetween. Hereinafter, like reference numerals refer to like elements. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be understood that the terms “comprises” and/or “comprising”, or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     Hereinafter, an electrode for a photoelectric conversion device and a photoelectric conversion device comprising the same according to an embodiment of the present invention will be described in detail with reference to  FIGS. 1 to 4 . 
       FIG. 1  is a sectional view schematically showing the entire configuration of a photoelectric conversion device according to an embodiment of the present invention.  FIG. 2  is a view schematically showing the state in which a dye is connected to an inorganic metal oxide semiconductor.  FIG. 3  is a plan view schematically showing a partial configuration of the photoelectric conversion device.  FIG. 4  is a sectional view schematically showing the structure of an electrode for a photoelectric conversion device according to an embodiment of the present invention. 
     Referring to  FIGS. 1 and 2 , a photoelectric conversion device  1  according to an embodiment of the present invention includes a first substrate  11 , a second substrate  11 ′, a first electrode  10 , a second electrode  10 ′, a photoelectrode layer  3 , a counter-electrode layer  7 , an electrolyte solution  5 , a sealing member  9  and extracting wires W. 
     The first and second substrates  11  and  11 ′ are disposed to oppose (or disposed to face) each other at a set or predetermined interval. The material of the first and second substrates  11  and  11 ′ can be any suitable transparent material having a low light absorption with respect to a spectrum or range from a visible region to a near infrared region of light (e.g., sunlight or the like) incident from the exterior of the photoelectric conversion device  1 . 
     For example, the material of the first and second substrates  11  and  11 ′ may include a glass material such as quartz, general glass, crown glass (borosilicate glass or BK7) or lead glass; a resin material such as polyethylene terephthalate, polyethylene naphthalate, polyimide, polyester, polyethylene, polycarbonate, polyvinylbutyrate, polypropylene, tetraacetylcellulose, syndiotactic polystyrene, polyphenylenesulfide, polyarylate, polysulfone, polyestersulfone, polyetherimide, annular polyolefin, phenoxy bromide or vinyl chloride; or the like. 
     In the first and second substrates  11  and  11 ′, a transparent conductive layer  13  formed into a film, for example, using a transparent conductive oxide (TCO) is formed on a surface of at least the first substrate  11  onto which external light is incident. The TCO can be any suitable conductive material having a low light absorption with respect to a spectrum or range from a visible region to a near infrared region of light incident from the exterior of the photoelectric conversion device  1 . For example, the TCO may be a metal oxide having excellent conductivity, such as indium tin oxide (ITO), tin oxide (SnO 2 ), fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO) or zinc oxide (ZnO 2 ). 
     In order to enhance photoelectric conversion efficiency, the surface resistance of the first and second electrodes  10  and  10 ′ should be as low as possible. 
     However, in the first and second substrates  11  and  11 ′, the second electrode  10 ′ formed on a surface of the second substrate  11 ′ opposite to (or facing away from) the first substrate  11  is not essential. In a case where the second electrode  10 ′ is formed on the surface of the second substrate  11 ′, it is not necessarily transparent. That is, the second electrode  10 ′ does not necessarily have a low absorption with respect to a spectrum or range from a visible region to a near infrared region of light incident from the exterior of the photoelectric conversion device  1 . 
     Also, detailed description of the first or second electrode  10  or  10 ′ according to this embodiment will be described later in more detail. 
     In the photoelectric conversion device  1 , the photoelectrode layer  3  is used as an inorganic metal oxide semiconductor layer having a photoelectric conversion function. The photoelectrode layer  3  is formed as a porous layer. 
     More specifically, as shown in  FIGS. 1 and 2 , the photoelectrode layer  3  is formed by stacking a plurality of metal oxide corpuscles  31  such as TiO 2  on the surface of the first electrode  10 . The metal oxide corpuscles  31  stacked as described above constitute a porous body, i.e., a nano-porous layer containing nano-meter pores therein. 
     As described above, the photoelectric layer  3  is formed as a porous body containing a plurality of micro-pores, so that it is possible to increase the surface area of the photoelectrode layer  3  and to connect a large amount of sensitizing dye  33  to the surface of the metal oxide corpuscle  31 . Accordingly, the photoelectric conversion device  1  can have high photoelectric conversion efficiency. 
     In the photoelectrode layer  3 , the sensitizing dye  33  is connected to the surface of the metal oxide corpuscle  31  with a linking group  35  interposed therebetween, thereby obtaining the photoelectrode layer in which inorganic metal oxide semiconductors are sensitized. 
     Also, the term “linking” refers to that the inorganic metal oxide semiconductor and the sensitizing dye are chemically or physically bonded to each other (e.g., bonding by absorption or the like). Therefore, the term “linking group” includes not only a chemical functional group but also an anchoring or adsorbing group. 
     Although  FIG. 2  shows a state in which only one sensitizing dye  33  is connected on the surface of the metal oxide corpuscle  31 , it is only a simple schematic view. In order to increase electrical power of the photoelectric conversion device  1 , it is preferable that the number of sensitizing dyes  33  connected to the surface of the metal oxide corpuscle  31  is as many as possible, and a large number of sensitizing dyes  33  are coated on the surface of the metal oxide corpuscle  31  as wide as possible. 
     However, in a case where the number of the coated sensitizing dyes is increased, excited electrons may be recombined by interaction between approaching sensitizing dyes  33 , and therefore, these electrons may not be extracted as electric energy. Hence, a co-adsorption substance such as deoxycholic acid may be used so that the sensitizing dyes  33  can be coated while maintaining an appropriate distance therebetween. 
     The photoelectrode layer  3  may be formed by stacking the metal oxide corpuscles  31  having a size of about 20 to 100 nm as a number-average particle size of a primary particle into a multi-layered structure. The thickness of the photoelectrode layer  3  may be a few μm (preferably, less than 10 μm). 
     If the thickness of the photoelectrode layer  3  is thinner than a few μm, light that transmits the photoelectrode layer  3  is increased, and the light excitation of the sensitizing dyes  33  is insufficient. Therefore, effective photoelectric conversion efficiency may not be obtained. 
     Also, if the thickness of the photoelectrode layer  3  is thicker than a few μm, the distance between the surface of the photoelectrode layer  3  (the surface that comes in contact with the electrolyte solution  5 ) and the electrical conducting surface (the interface between the photoelectrode layer  3  and the first electrode  10 ) is lengthened. Therefore, since it is difficult that excited electrons are effectively transferred to the electrical conducting surface, satisfactory photoelectric conversion efficiency may not be obtained. 
     Next, the metal oxide corpuscle  31  and the sensitizing dye  33 , available for the photoelectrode layer  3  according to an embodiment of the present invention, will be described in more detail. 
     Generally, the inorganic metal oxide semiconductor has a photoelectric conversion function for light in a partial wavelength region. However, the sensitizing dye  33  is connected to the surface of the metal oxide corpuscle  31 , so that photoelectric conversion is possible with respect to light in a spectrum or range from a visible region to a near infrared region. 
     A compound available for the metal oxide corpuscle  31  is not particularly limited as long as it is a compound that connects the sensitizing dye  33  and has a sensitized photoelectric conversion function. For example, the compound may include titanium oxide, tin oxide, tungsten oxide, zinc oxide, indium oxide, niobium oxide, iron oxide, nickel oxide, cobalt oxide, strontium oxide, tantalum oxide, antimony oxide, lanthanide oxide, yttrium oxide, vanadium oxide, or the like. 
     Here, since the surface of the metal oxide corpuscle  31  is sensitized by the sensitizing dye  33 , the conduction band of the inorganic metal oxide may exist at a position at which it easily receives electrons from the optical excitation trap of the sensitizing dye  33 . 
     In this viewpoint, the compound used as the metal oxide corpuscle  31  may include titanium oxide, tin oxide, zinc oxide, niobium oxide or the like. In the viewpoint of price, environment or the like, the compound used as the metal oxide corpuscle  31  may include titanium oxide. 
     The sensitizing dye  33  is not particularly limited as long as it is a dye having a photoelectric conversion function with respect to light in a set spectrum or range (e.g., in a spectrum or range from a visible region to a near infrared region). For example, the sensitizing dye  33  may include an azo-based dye, a quinacridone-based dye, a diketopyrrolopyrrole-based dye, a squarylium-based dye, a cyanine-based dye, a merocyanine-based dye, a triphenylmethane-based dye, a xanthene-based dye, a porphyrin-based dye, a chlorophyll-based dye, a ruthenium complex-based dye, an indigo-based dye, a perylene-based dye, a dioxadine-based dye, an anthraquinone-based dye, a phthalocyanine-based dye, a naphthalocyanine-based dye, a derivative thereof, or the like. 
     The sensitizing dye  33  may include a functional group connectable to the surface of the metal oxide corpuscle  31  as the linking group so that excitation electrons of the optically excited dye can be rapidly transferred to the conduction band of the inorganic metal oxide. 
     The functional group is not particularly limited as long as it is a substituting group having a function that connects the sensitizing dye  33  to the surface of the metal oxide corpuscle  31  and rapidly transfers the excitation electrons of the dye to the conduction band of the inorganic metal oxide. For example, the functional group may include a carboxyl group, a hydroxyl group, a hydroxamic acid group, a sulfinyl group, a phosphonic acid group, a phosphinic acid group, or the like. 
     The counter-electrode layer  7  serves as a positive electrode of the photoelectric conversion device  1 . The counter-electrode layer  7  is formed as a film on the surface of the second substrate  11 ′ with the second electrode  10 ′ formed thereon, opposing or facing the first substrate  11  with the first electrode  10  formed thereon. 
     That is, the counter-electrode layer  7  is disposed on the surface of the second electrode  10 ′ to be opposite to the photoelectrode layer  3  in a region surrounded by the first electrode  10 , the second electrode  10 ′ and the sealing member  9 . 
     A metal catalyst layer having conductivity is disposed on a surface of the counter-electrode layer  7  (a side of the counter-electrode layer  7 , opposite to the photoelectrode layer  3 ). 
     For example, the conductive material available for the counter-electrode layer  7  may include metal (platinum, gold, silver, copper, aluminum, rhodium, indium or the like), metal oxide (indium tin oxide (ITO)), tin oxide (including tin oxide doped with fluorine or the like), zinc oxide, conductive carbon material, conductive organic material, or the like. 
     The thickness of the counter-electrode layer  7  is not particularly limited. For example, the thickness of the counter-electrode layer  7  may be at or between 5 nm and 10 μm. 
     Also, the extracting wires W are respectively connected to the counter-electrode layer  7  and the first electrode  10  of the side at which the photoelectrode layer  3  is formed. The extracting wire W from the first electrode  10  and the extracting wire W from the counter-electrode layer  7  are connected to each other at the exterior of the photoelectric conversion device  1 . 
     The first electrode  10  and the counter-electrode layer  7  may be isolated from each other so as to be sealed by the sealing member  9  while being spaced apart from each other. 
     The sealing member  9  is formed along outer circumferential portions of the first electrode  10  and the counter-electrode layer  7 . The sealing member  9  may function to seal a space between the first electrode  10  and the counter-electrode layer  7 . 
     A resin having high sealing performance and corrosion resistance may be used as the sealing member  9 . For example, the resin may include thermoplastic resin, photocurable resin, ionomer resin, glass frit, or the like, which are formed in a film shape. 
     Also, the electrolyte solution  5  is injected into the space between the first electrode  10  and the counter-electrode layer  7  and then sealed by the sealing member  9 . 
     For example, the electrolyte solution  5  includes an electrolyte, a medium and an additive. 
     Here, the electrolyte may include a redox electrolyte such as an I 3   − /I −  or Br 3   − /Br −  series, or the like. For example, the electrolyte may include a mixture of I 2  and iodide (Lil, Nal, Kl, Csl, MgI 2 , CuI, tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide and the like), a mixture of Br 2  and bromide (LiBr and the like), an organic molten salt compound, and the like. However, the substance used as the electrolyte is not limited thereto. 
     The aforementioned iodide, bromide or the like may be used singly or in combinations thereof. 
     Particularly, the electrolyte may include a mixture of I 2  and iodide (e.g., I 2  and Lil), and an electrolyte mixed with pyridinium iodide, imidazolium iodide or the like. However, the electrolyte is not limited thereto. 
     In the electrolyte solution  5 , the concentration of the I 2  may be at or between 0.01 and 0.5 M, and any one or both of the iodide and bromide (in the combinations thereof) may be at or between 0.1 to 15 M. 
     The medium used in the electrolyte solution  5  may be a compound capable of realizing excellent ion conductivity. The medium may include a liquid-phase medium, a solid-phase medium or an ionic liquid. 
     Various suitable kinds of additives may be added into the electrolyte solution  5  so as to enhance the durability of the photoelectric conversion device  1  or electric power. 
     The thickness of the layer put and sealed in the electrolyte solution  5  is not particularly limited. However, the layer may be formed to have a thickness in which the counter-electrode layer  7  does not come in direct contact with the photoelectrode layer  3  having the adsorbed dye. Specifically, the thickness of the layer may be at or between 0.1 and 100 μm. 
     In the photoelectrode layer  3  including the metal oxide corpuscle  31  and the sensitizing dye  33  connected to the surface of the metal oxide corpuscle  31  with the linking group  35  interposed therebetween, light comes in contact with the sensitizing dye  33  connected to the surface of the metal oxide corpuscle  31  as illustrated in  FIG. 2 . Then, the sensitizing dye  33  is in an excitation state and emits optically excited electrons. The emitted excitation electrons are transferred to the conduction band of the metal oxide corpuscle  31  through the linking group  35 . 
     The excitation electrons that approach the metal oxide corpuscle  31  are transferred to another metal oxide corpuscle  31  to approach the first electrode  10 , and flow out to the exterior of the photoelectric conversion device  1  through the extracting wire W. 
     Also, the sensitizing dye  33  that is in a state in which electrons are deficient due to the emitted excitation electrons receives electrons supplied from the counter-electrode layer  7  through the electrolyte such as I 3   − /I −  in the electrolyte solution  5 , and thus, returns to an electrically neutral state. 
     Hereinafter, the configuration of an electrode for a photoelectric conversion device according to embodiments of the present invention will be described in more detail with reference to  FIGS. 1 ,  3  and  4  to  7 . 
       FIG. 1  is a sectional view schematically showing the entire configuration of a photoelectric conversion device according to an embodiment of the present invention.  FIG. 3  is a plan view schematically showing a partial configuration of the photoelectric conversion device.  FIG. 4  is a sectional view schematically showing the structure of an electrode for the photoelectric conversion device according to a first embodiment of the present invention.  FIG. 5  is a sectional view schematically showing the structure of an electrode for the photoelectric conversion device according to a second embodiment of the present invention.  FIG. 6  is a sectional view schematically showing the structure of an electrode for the photoelectric conversion device according to a third embodiment of the present invention.  FIG. 7  is a sectional view schematically showing the structure of an electrode for a photoelectric conversion device according to a fourth embodiment of the present invention. For convenience purposes, the following description discloses in detail a first electrode  10  and a first substrate  11 . However, it should be apparent that in the following description, the first electrode (the electrode)  10  ( 10 ′) can refer to the first electrode  10  or the second electrode  10 ′ as shown in  FIG. 1 , and the first substrate (the substrate)  11  ( 11 ′) can refer to the first substrate  11  or the second substrate  11 &#39;s as shown in  FIG. 1 . 
     Referring to  FIG. 4 , a first electrode  10  (or electrode  10 ′) for the photoelectric conversion device  1  according to the first embodiment of the present invention includes a transparent conductive layer  13  that is formed on a first substrate  11  (or substrate  11 ′) and has spacing regions L 1  formed at a set or predetermined interval; a metal electrode layer  15   a  formed in a corresponding one of the spacing regions L 1 ; and protection layer  17  that is formed on the transparent conductive layer  13  and the metal electrode layer  15   a  to cover the metal electrode layer  15   a.    
     Here, groove portions H 1  each having a set or predetermined pattern are formed in the first substrate  11 , and the positions of the groove portions H 1  are formed to correspond to the respective spacing regions L 1  formed at the set or predetermined interval in the transparent conductive layer  13 . Although the groove portions H 1  may be formed using a physical or chemical etching method, the method of forming the groove portions H 1  is not limited thereto. For example, an etching method using laser may be used as the physical etching method, and a method of performing liquid or vapor phase etching after using a photolithography technique may be used as the chemical etching method. Alternatively, a combination of the physical and chemical etching methods may be used as the etching method. 
     The material of the first substrate  11  can be any suitable transparent material having a low light absorption with respect to a spectrum or range from a visible region to a near infrared region of light (sunlight or the like) incident from the exterior of the photoelectric conversion device  1 . Examples of the material available for the first substrate  11  are identical (or substantially identical) to those described above, and therefore, will not be provided again. 
     The transparent conductive layer  13  is formed on the first substrate  11  and patterned to have the spacing regions L 1  at the set or predetermined interval. The transparent conductive layer  13  is formed as a film using a transparent conductive oxide (TOC). The material of the transparent conductive layer  13  is not particularly limited as long as it is a conductive material having a low light absorption with respect to a spectrum or range from a visible region to a near infrared region of light incident from the exterior of the photoelectric conversion device  1 . Examples of the material available for the transparent conductive layer  13  are identical (or substantially identical) to those described above, and therefore, will not be provided again. 
     Referring to  FIG. 4 , the metal electrode layer  15   a  is formed to have patterns corresponding to the patterns of the respective groove portions H 1  formed in the first substrate. As described above, the positions of the groove portions H 1  are formed to match or correspond to the respective spacing regions L 1  formed in the transparent conductive layer  13 . In one embodiment, the height of an upper or top surface of the metal electrode layer  15   a  is formed to be between the height of an upper or top surface of the first substrate  11  and the height of an upper or top surface of the transparent conductive layer  13 . Preferably, the upper or top surface of the metal electrode layer  15   a  is formed to have a height identical to the upper or top surface of the transparent conductive layer  13  or to have a height slightly lower than the upper or top surface of the transparent conductive layer  13 . 
     The metal electrode layer  15   a  functions to transfer excitation electrons to the extracting wire W. Here, the excitation electrons are transferred through the metal oxide corpuscles  31  to approach the first electrode  10 . The metal electrode layer  15   a  is a metal wire formed on the surface of the first electrode  10 . 
     The metal electrode layer  15   a  is formed to prevent a phenomenon in which the surface resistance of the first electrode  10  is generally high (about 10 Ω/sq or higher), the generated current is converted into Joule heat in a base material having relatively low conductivity, such as the transparent conductive layer  13 , and therefore, photoelectric conversion efficiency is lowered. 
     Accordingly, the metal electrode layer  15   a  is electrically connected to the first electrode  10 . The material of the metal electrode layer  15   a  may include a high-conductive metal such as Ag, Ag/Pd, Cu, Au, Ni, Ti, Co, Cr or Al, an alloy thereof, a material such as glass frit, or an alloy of the metal. 
     The shape of the pattern of the metal electrode layer  15   a  in a plane direction is not particularly limited as long as it reduces the loss of electrical energy. That is, the pattern of the metal electrode layer  15   a  may be formed in any suitable shape such as a lattice shape, a stripe shape, a rectangular shape, or a comb (teeth) shape. 
     As described above, the pattern of the metal electrode layer  15   a  according to the first embodiment of the present invention is formed to match or correspond to the pattern of the respective groove portions H 1  formed in the first substrate  11 . In this instance, the cross-section of the pattern of the metal electrode layer  15   a  in the thickness direction of the first substrate  11  has a triangle shape (e.g., a plurality of triangles). 
     Referring to  FIG. 5 , the metal electrode layer  15   b  according to the second embodiment of the present invention is formed to have a pattern matching or corresponding to the pattern of respective groove portions H 2  formed in a first substrate  11 . As described above, the positions of the groove portions H 2  are formed to match or correspond to respective spacing regions L 2  formed in a transparent conductive layer  13 . In this instance, the cross-section of the pattern of the metal electrode layer  15   b  in the thickness direction of the first substrate  11  may have a rectangle shape (e.g., a plurality of rectangles) unlike the first embodiment. 
     As shown in  FIG. 6 , the metal electrode layer  15   c  according to the third embodiment of the present invention is formed to have a pattern matching or corresponding to the pattern of respective groove portions H 3  formed in a first substrate  11 . As described above, the positions of the groove portions H 3  are formed to match or correspond to respective spacing regions L 3  formed in a transparent conductive layer  13 . In this instance, the cross-section of the pattern of the metal electrode layer  15   c  in the thickness direction of the first substrate  11  may have a circle shape (e.g., a plurality of half-circles) unlike the first and second embodiments. That is, the cross-section of the pattern of the metal electrode layer  15   c  may have various suitable shapes, such as a polygon shape, a polygonal cone shape, an ellipse shape, or a circle shape. 
     In one embodiment, the height of each of the metal electrode layers  15   a ,  15   b  and  15   c  according to the first to third embodiments of the present invention is formed to be between the height of an upper surface of the first substrate  11  and the height of an upper surface of the transparent conductive layer  13 . Preferably, each of the metal electrode layers  15   a ,  15   b  and  15   c  according to the first to third embodiments of the present invention is formed to have a height identical to the upper surface of the transparent conductive layer  13  or to have a height slightly lower than the upper surface of the transparent conductive layer  13 . 
     As shown in  FIG. 7 , the metal electrode layer  15   d  according to the fourth embodiment of the present invention is formed in spacing regions L 4  formed at a set or predetermined interval in a transparent conductive layer  13  on a first substrate  11 , respectively. That is, the first substrate  11  according to the fourth embodiment of the present invention is not provided with the groove portions H 1 , H 2  and H 3  in the first to third embodiments. Accordingly, a lower or bottom surface of the metal electrode layer  15   d  comes in contact with an upper or top surface of the first substrate  11 . 
     Here, the metal electrode layer  15   a  is formed of a metal such as Ag, Ag/Pd, Cu, Au, Ni, Ti, Co, Cr or Al, as described above. Hence, the metal electrode layer  15   a  may be corroded by the electrolyte solution containing iodine (I 3   − /I −  or the like). Accordingly, the photoelectric conversion device  1  according to the embodiment of the present invention includes a protection layer  17  which will be described below in more detail. 
     The protection layer  17  functions to prevent or restrain corrosion caused by the electrolyte solution  5  of each of the metal electrode layers  15   a ,  15   b ,  15   c  and  15   d . The protection layer  17  is positioned on the transparent conductive layer  13  and each of the metal electrode layers  15   a ,  15   b ,  15   c  and  15   d  to coat the exposed surface of each of the metal electrode layers  15   a ,  15   b ,  15   c  and  15   d , thereby protecting each of the metal electrode layers  15   a ,  15   b ,  15   c  and  15   d  from the corrosion caused by the electrolyte solution  5 . Here, the protection layer  17  is obtained by coating and sintering a glass paste with a low melting point on the exposed surface of each of the metal electrode layers  15   a ,  15   b ,  15   c  and  15   d . In one embodiment, the protection layer  17  has a thickness at or between 10 and 50 μm. Preferably, the protection layer  17  has a thickness of more than 20 μm so as to prevent a defect such as a pin hole. 
     If a comparable metal electrode layer is protruded from a substrate, the interface between regions has a very large step difference. In one region, the protruded metal electrode layer is formed, and the protection layer is formed on the metal electrode layer. In another region, only the protruded metal electrode layer is formed, and the protection layer is not formed on the metal electrode layer. Here, the protection layer is not formed on a lower or bottom surface of the sealing member, and the adhesion of the sealing member may be degraded or the sealing member may get loose due to the protruded metal electrode layer itself. Therefore, there is a problem in view of the reliability of products. 
     However, as described in the first to fourth embodiments, the height of the upper surface of each of the metal electrode layers  15   a ,  15   b ,  15   c  and  15   d  is formed to be between the height of the upper surface of the first substrate  11  and the height of the upper surface of the transparent conductive layer  13 , i.e., to be buried or embedded in the first substrate  11  and/or the transparent conductive layer  13 . Accordingly, the aforementioned step difference can be reduced. 
     Referring to  FIG. 3 , the protection layer  17  according to an embodiment of the present invention is formed on the exposed surface of the metal electrode layer  15  in the region which has the electrolyte solution  5  injected thereinto and is sealed by the sealing member  9 , and is not formed on the exposed surface of the metal electrode layer  15  formed at the outside of the region sealed by the sealing member  9 . As the metal electrode layer  15  has a structure in which the step difference is reduced, the leakage of the electrolyte solution  5  due to the degradation of the adhesion of the sealing member or the looseness of the sealing member is reduced, thereby enhancing the reliability of products. 
     In a case where the metal electrode layer  15  has a rectangular shape, three surfaces of the metal electrode layer  15  were conventionally exposed. On the other hand, if the metal electrode layer  15  according to the embodiment of the present invention is formed to be buried or embedded in the first substrate  11  and/or the transparent conductive layer  13 , only the upper surface of the metal electrode layer  15  is exposed. Thus, it is possible to decrease the possibility of corrosion of the metal electrode layer  15 , which may be caused by the crack or looseness of the protection layer  17 . 
     The glass paste composite used in the protection layer  17  is a paste composite including glass frit, binder resin, solvent, additive, or the like. The glass paste composite is coated on the metal electrode layer  15  buried or embedded in the first substrate  11  and/or the transparent conductive layer  13  and then sintered, thereby forming the protection layer  17 . Here, the glass frit used in the glass paste composite may include at least one of alumina, zirconium oxide, silica, silicate, phosphate, colloidal silica, alkyl silicate, boron oxide, bismuth oxide, zinc oxide and metal alkoxide. 
     As described above, according to the embodiments of the present invention, the shape of a protruded electrode is improved, so that the reliability of products can be enhanced through a simple process. 
     Also, as the metal electrode layer has a structure in which the step difference is reduced as described above, the leakage of the electrolyte solution due to the degradation of the adhesion of the sealing member or the looseness of the sealing member can be reduced, thereby enhancing the reliability of products. 
     Also, while three surfaces of the metal electrode layer were conventionally exposed, only the upper surface of the metal electrode layer is exposed. Thus, it is possible to decrease the possibility of corrosion of the metal electrode layer, which may be caused by the crack or looseness of the protection layer. 
     While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.