Patent Publication Number: US-2012037216-A1

Title: Conductive paste and electronic device and solar cell including an electrode formed using the conductive paste

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Korean Patent Application No. 10-2010-0078344, filed on Aug. 13, 2010, and all the benefits accruing therefrom under 35 U.S.C. §119, the content of which in its entirety is herein incorporated by reference. 
     BACKGROUND 
     1. Field 
     This disclosure relates to a conductive paste, and an electronic device and a solar cell including an electrode formed using the conductive paste. 
     2. Description of the Related Art 
     A solar cell is a photoelectric conversion device that transforms solar energy into electrical energy. Solar cells have attracted much attention as a potentially infinite and essentially pollution-free next generation energy source. 
     A solar cell includes p-type and n-type semiconductors. When an electron-hole pair (“EHP”) is produced by light absorbed in a photoactive layer of the semiconductors, the solar cell produces electrical energy by transferring electrons and holes to the n-type and p-type semiconductors, respectively, and then collects the electrons and the holes in respective electrodes of the solar cell. 
     A solar cell desirably has as high efficiency as possible for producing electrical energy from solar energy. In order to improve this efficiency, the solar cell desirably absorbs light with minimal loss, so that it may produce as many electron-hole pairs as possible, and then collect the produced charges without significant loss. 
     An electrode may be fabricated using a deposition method, which may include a complicated process, have a high cost, and can take a long time. Accordingly, a simplified process, such as screen printing a conductive paste including a conductive material, has been suggested. However, an electrode formed using a conductive paste may have low conductivity because of a glass frit included in a conductive paste. Thus there remains a need for an improved conductive paste. 
     SUMMARY 
     An aspect of this disclosure provides a conductive paste which is capable of improving conductivity of an electrode. 
     Another aspect of this disclosure provides an electronic device including an electrode including the fired conductive paste. 
     Yet another aspect of this disclosure provides a solar cell including an electrode including the fired conductive paste. 
     According to an aspect of this disclosure, disclosed is a conductive paste including a conductive powder, a metallic glass, and an organic vehicle. Herein, the metallic glass includes an alloy of at least two metals selected from a first metal having a low resistivity, a second metal which forms a solid solution with the conductive powder, a third metal which extends a supercooled liquid region of the metallic glass, and a fourth metal having a higher standard free energy of formation of oxide than a standard free energy of formation of oxide of each of the first, the second, and the third metals when present. 
     The first metal may have resistivity of less than about 100 microohm-centimeters (“μΩcm”). 
     The first metal may have resistivity of less than about 15 μΩcm. 
     The first metal may beat least one selected from silver (Ag), copper (Cu), gold (Au), aluminum (Al), calcium (Ca), beryllium (Be), magnesium (Mg), sodium (Na), molybdenum (Mo), tungsten (W), tin (Sn), zinc (Zn), nickel (Ni), potassium (K), lithium (Li), iron (Fe), palladium (Pd), platinum (Pt), rubidium (Rb), chromium (Cr), and strontium (Sr). 
     The second metal may have a heat of mixing with the conductive powder of less than 0 kJ/mol. 
     The conductive powder may include silver (Ag), and the second metal may be at least one selected from lanthanum (La), cerium (Ce), praseodymium (Pr), promethium (Pm), samarium (Sm), lutetium (Lu), yttrium (Y), neodymium (Nd), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), thorium (Th), calcium (Ca), scandium (Sc), barium (Ba), ytterbium (Yb), strontium (Sr), europium (Eu), zirconium (Zr), lithium (Li), hafnium (Hf), magnesium (Mg), phosphorus (P), arsenic (As), palladium (Pd), gold (Au), plutonium (Pu), gallium (Ga), germanium (Ge), aluminum (Al), zinc (Zn), antimony (Sb), silicon (Si), tin (Sn), titanium (Ti), cadmium (Cd), indium (In), platinum (Pt), and mercury (Hg). 
     The third metal may reduce the glass transition temperature (“Tg”) of the metallic glass or increase the crystallization temperature (“Tc”) of the metallic glass. 
     The metallic glass may include copper (Cu) and zirconium (Zr), and the third metal may include at least one selected from aluminum (Al), silver (Ag), nickel (Ni), titanium (Ti), iron (Fe), and hafnium (Hf). 
     The third metal may be included in an amount of about 10 atomic percent (at %) or less, based on the total amount of the metallic glass. 
     The metallic glass may have a supercooled liquid region of about 5° C. to about 200° C. 
     The fourth metal may have an absolute value of a Gibbs free energy of metal oxide formation greater than an absolute value of a Gibbs free energy of metal oxide formation of each of the first, the second, and the third metals, if present. 
     The fourth metal may have an absolute value of a Gibbs free energy of metal oxide formation of about 100 kiloJoules per mole (kJ/mol) or greater. 
     The conductive powder, the metallic glass, and the organic vehicle may be included in an amount of about 30 to about 98 weight percent (wt %), about 1 to about 50 wt %, and about 69 to about 1 wt %, respectively, based on the total weight of the conductive paste, respectively. 
     According to another aspect of the disclosure, an electronic device includes an electrode including a fired conductive paste including a conductive powder, a metallic glass, and an organic vehicle. Herein, the metallic glass is an alloy of at least two metals selected from a first metal having a low resistivity, a second metal which forms a solid solution with the conductive powder, a third metal which extends a supercooled liquid region of the metallic glass, and a fourth metal having a higher standard free energy of formation of oxide than a standard free energy of formation of oxide of each of the first, the second, and the third metals when present. 
     The first metal may have resistivity of less than about 100 μΩcm, and the second metal may have a heat of mixing with the conductive powder of less than 0 kJ/mol. 
     The third metal may reduce a glass transition temperature (“Tg”) of the metallic glass or increase the crystallization temperature (“Tc”) of the metallic glass, and the fourth metal may have an absolute value of a Gibbs free energy of metal oxide formation greater than an absolute value of a Gibbs free energy of metal oxide formation of each of the first, the second, and the third metals when present. 
     According to another aspect of the disclosure, a solar cell includes a semiconductor layer and an electrode electrically connected with the semiconductor layer and including a fired conductive paste including a conductive powder, a metallic glass, and an organic vehicle, wherein, the metallic glass is an alloy of at least two metals selected from a first metal having a low resistivity, a second metal which forms a solid solution with the conductive powder, a third metal which extends a supercooled liquid region of the metallic glass, and a fourth metal having a higher standard free energy of formation of oxide than a standard free energy of formation of oxide of each of the first, the second, and the third metals when present. 
     The first metal may have resistivity of less than about 100 μΩcm, and the second metal may have a heat of mixing with the conductive powder of less than 0 kJ/mol. 
     The first metal may be at least one selected from silver (Ag), copper (Cu), gold (Au), aluminum (Al), calcium (Ca), beryllium (Be), magnesium (Mg), sodium 
     (Na), molybdenum (Mo), tungsten (W), tin (Sn), zinc (Zn), nickel (Ni), potassium (K), lithium (Li), iron (Fe), palladium (Pd), platinum (Pt), rubidium (Rb), chromium (Cr), and strontium (Sr). 
     The conductive powder may include silver (Ag), and the second metal may be at least one selected from lanthanum (La), cerium (Ce), praseodymium (Pr), promethium (Pm), samarium (Sm), lutetium (Lu), yttrium (Y), neodymium (Nd), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), thorium (Th), calcium (Ca), scandium (Sc), barium (Ba), ytterbium (Yb), strontium (Sr), europium (Eu), zirconium (Zr), lithium (Li), hafnium (Hf), magnesium (Mg), phosphorus (P), arsenic (As), palladium (Pd), gold (Au), plutonium (Pu), gallium (Ga), germanium (Ge), aluminum (Al), zinc (Zn), antimony (Sb), silicon (Si), tin (Sn), titanium (Ti), cadmium (Cd), indium (In), platinum (Pt), and mercury (Hg). 
     The third metal may reduce the glass transition temperature (“Tg”) of the metallic glass or increase a crystallization temperature (“Tc”) of the metallic glass, and the fourth metal may have an absolute value of a Gibbs free energy of metal oxide formation greater than an absolute value of a Gibbs free energy of metal oxide formation of each of the first, the second, and the third metals. 
     According to yet another aspect of the disclosure, a solar cell includes a semiconductor layer, an electrode including a conductive material and electrically connected with the semiconductor layer, and a buffer layer contacting the semiconductor layer and the electrode. Herein, the buffer layer may include an alloy of at least two metals selected from a first metal having a low resistivity, a second metal which forms a solid solution with the conductive powder, a third metal which extends a supercooled liquid region of a metallic glass of the buffer layer, and a fourth metal having a higher standard free energy of formation of oxide than a standard free energy of formation of oxide of each of the first, the second, and the third metals if present. 
     The buffer layer may further include a crystallized conductive material. 
     The conductive material may be included in at least one of the semiconductor layer and the buffer layer. 
     The first metal may have resistivity of less than about 100 μΩcm, and the second metal may have a heat of mixing with the conductive powder of less than 0 kJ/mol. 
     The first metal may be at least one selected from silver (Ag), copper (Cu), gold (Au), aluminum (Al), calcium (Ca), beryllium (Be), magnesium (Mg), sodium (Na), molybdenum (Mo), tungsten (W), tin (Sn), zinc (Zn), nickel (Ni), potassium (K), lithium (Li), iron (Fe), palladium (Pd), platinum (Pt), rubidium (Rb), chromium (Cr), and strontium (Sr). 
     The conductive powder may include silver (Ag), and the second metal may be at least one selected from lanthanum (La), cerium (Ce), praseodymium (Pr), promethium (Pm), samarium (Sm), lutetium (Lu), yttrium (Y), neodymium (Nd), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), thorium (Th), calcium (Ca), scandium (Sc), barium (Ba), ytterbium (Yb), strontium (Sr), europium (Eu), zirconium (Zr), lithium (Li), hafnium (Hf), magnesium (Mg), phosphorus (P), arsenic (As), palladium (Pd), gold (Au), plutonium (Pu), gallium (Ga), germanium (Ge), aluminum (Al), zinc (Zn), antimony (Sb), silicon (Si), tin (Sn), titanium (Ti), cadmium (Cd), indium (In), platinum (Pt), and mercury (Hg). 
     The third metal may reduce the glass transition temperature (“Tg”) of the metallic glass or increase a crystallization temperature (“Tc”) of the metallic glass, and the fourth metal may have an absolute value of a Gibbs free energy of metal oxide formation greater than an absolute value of a Gibbs free energy of metal oxide formation of each of the first, the second, and the third metals, if present. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, advantages and features of this disclosure will become more apparent by describing in further detail exemplary embodiments thereof with reference to the accompanying drawings, in which: 
         FIGS. 1 to 3  are a schematic diagram of an embodiment of heat treating a conductive powder and a metallic glass on a semiconductor substrate; 
         FIGS. 4A to 4C  are a schematic diagram showing an expanded view of region A of  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of an embodiment of a solar cell; and 
         FIG. 6  is a cross-sectional view of another embodiment of a solar cell. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments will hereinafter be described in further detail with reference to the accompanying drawings, in which various embodiments are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, “a first element,” “component,” “region,” “layer,” or “section” discussed below could be termed a second element, component, region, layer, or section without departing from the teachings herein. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. 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 further 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. The term “at least one” means a combination comprising one or more of the listed components may be used. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Exemplary embodiments are described herein with reference to cross section illustrations that are schematic illustrations of idealized embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present claims. 
     “Alkyl” means a straight or branched chain saturated aliphatic hydrocarbon having 1 to 12 carbon atoms, more specifically 1 to 6 carbon atoms. 
     Herein, the term ‘metal’ refers to a metal and a semimetal. 
     First, disclosed is a conductive paste. 
     The conductive paste according to an embodiment includes a conductive powder, a metallic glass, and an organic vehicle. 
     The conductive powder may comprise at least one metal or alloy selected from an aluminum (Al)-containing metal such as aluminum or an aluminum alloy, a silver (Ag)-containing metal such as silver or a silver alloy, a copper (Cu)-containing metal such as copper (Cu) or a copper alloy, a nickel (Ni)-containing metal such as nickel (Ni) or a nickel alloy. However, the conductive powder is not limited thereto but may include other metals, an additive that is not the metal or alloy. 
     The conductive powder may have a size (e.g., average largest particle size) ranging from about 0.1 to 50 micrometers (μm), specifically about 0.5 to about 40 μm, more specifically about 1 to about 30 μm. Particles of the conductive powder may be irregular, or have a spherical, rod-like, or plate-like shape. 
     The metallic glass includes an alloy having a disordered atomic structure including two or more metals. The metallic glass may be an amorphous metal. The metallic glass may have about 50 to about 100 weight percent (“wt %”), specifically about 70 to about 100 wt %, more specifically about 90 to about 100 wt % amorphous content, based on a total weight of the metallic glass. Because the metallic glass has a low resistivity, and thus is different from an insulating glass such as a silicate, it may be considered to be an electrical conductor at a voltage and a current of a solar cell. 
     The metallic glass is an alloy of at least two metals selected from a first metal which has a low resistivity, a second metal which is capable of forming a solid solution with the conductive powder, a third metal which is capable of extending a supercooled liquid region of the metallic glass, or a fourth metal having a higher standard free energy of formation of oxide than each of the first, the second, or the third metals when the first, second, or third metals is present in the metallic glass. 
     The first metal, which has a low resistivity, may substantially determine the conductivity of the metallic glass. The first metal may have a resistivity of less than about 100 microohm-centimeters (μΩcm), specifically about 0.001 to about 90 μΩcm, more specifically about 0.01 to about 50 μΩcm. In an embodiment, the first metal may have resistivity of less than about 15 μΩcm. 
     The first metal may be, for example, at least one selected from silver (Ag), copper (Cu), gold (Au), aluminum (Al), calcium (Ca), beryllium (Be), magnesium (Mg), sodium (Na), molybdenum (Mo), tungsten (W), tin (Sn), zinc (Zn), nickel (Ni), potassium (K), lithium (Li), iron (Fe), palladium (Pd), platinum (Pt), rubidium (Rb), chromium (Cr), and strontium (Sr). 
     The second metal is capable of forming a solid solution with the conductive powder when present in the metallic glass. 
     When the metallic glass is heated to a temperature which is higher than a glass transition temperature (Tg) of the metallic glass, it may be soft, like glass, and show a liquid-like behavior. Herein, because the metallic glass includes a second metal which is capable of forming a solid solution with the conductive powder, the conductive powder may diffuse into the softened metallic glass. 
     For example, when the conductive paste including the metallic glass is disposed on a semiconductor substrate to form an electrode for a solar cell, the metallic glass becomes soft during the heat treatment. In addition, during the heat treatment, particles of the conductive powder form a solid solution with the second metal when it is included in the metallic glass, and thus the particles of the conductive powder diffuse into the softened metallic glass. 
     Finally, the particles of the conductive powder may diffuse into the semiconductor substrate through the softened metallic glass when the second metal is present. Accordingly, after cooling, crystallized particles of the conductive powder are produced at or near the surface of the semiconductor substrate in a large amount. In this way, the crystallized particles of the conductive powder formed at or near the surface of the semiconductor substrate may improve the transfer of charges produced in the semiconductor substrate by solar cell, thereby improving efficiency of the solar cell. 
     The second metal which is capable of forming a solid solution with a conductive powder may be selected from metals having a heat of mixing (“Hm”) of less than 0 kiloJoules per mole (kJ/mol), specifically less than −0.1 kJ/mol, more specifically less than −0.5 kJ/mol with the conductive powder. 
     For example, when the conductive powder includes silver (Ag), the second metal may include, for example, lanthanum (La), cerium (Ce), praseodymium (Pr), promethium (Pm), samarium (Sm), lutetium (Lu), yttrium (Y), neodymium (Nd), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), thorium (Th), calcium (Ca), scandium (Sc), barium (Ba), ytterbium (Yb), strontium (Sr), europium (Eu), zirconium (Zr), lithium (Li), hafnium (Hf), magnesium (Mg), phosphorus (P), arsenic (As), palladium (Pd), gold (Au), plutonium (Pu), gallium(Ga), germanium (Ge), aluminum (Al), zinc (Zn), antimony (Sb), silicon (Si), tin (Sn), titanium (Ti), cadmium (Cd), indium(In), platinum (Pt), or mercury (Hg). The heat of mixing of representative combinations of a second metal with Ag are listed in the following Table 1. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Hm 
                   
                 Hm 
                   
                 Hm 
               
               
                 X—Ag 
                 (kJ/mol) 
                 X—Ag 
                 (kJ/mol) 
                 X—Ag 
                 (kJ/mol) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 La—Ag 
                 −30 
                 Nd—Ag 
                 −29 
                 Th—Ag 
                 −29 
               
               
                 Ce—Ag 
                 −30 
                 Gd—Ag 
                 −29 
                 Ca—Ag 
                 −28 
               
               
                 Pr—Ag 
                 −30 
                 Tb—Ag 
                 −29 
                 Sc—Ag 
                 −28 
               
               
                 Pm—Ag 
                 −30 
                 Dy—Ag 
                 −29 
                 Ba—Ag 
                 −28 
               
               
                 Sm—Ag 
                 −30 
                 Ho—Ag 
                 −29 
                 Yb—Ag 
                 −28 
               
               
                 Lu—Ag 
                 −30 
                 Er—Ag 
                 −29 
                 Sr—Ag 
                 −27 
               
               
                 Y—Ag 
                 −29 
                 Tm—Ag 
                 −29 
                 Eu—Ag 
                 −27 
               
               
                 Zr—Ag 
                 −20 
                 Au—Ag 
                 −6 
                 Si—Ag 
                 −3 
               
               
                 Li—Ag 
                 −16 
                 Pu—Ag 
                 −6 
                 Sn—Ag 
                 −3 
               
               
                 Hf—Ag 
                 −13 
                 Ga—Ag 
                 −5 
                 Ti—Ag 
                 −2 
               
               
                 Mg—Ag 
                 −10 
                 Ge—Ag 
                 −5 
                 Cd—Ag 
                 −2 
               
               
                 P—Ag 
                 −10 
                 Al—Ag 
                 −4 
                 In—Ag 
                 −2 
               
               
                 As—Ag 
                 −8 
                 Zn—Ag 
                 −4 
                 Pt—Ag 
                 −1 
               
               
                 Pd—Ag 
                 −7 
                 Sb—Ag 
                 −4 
                 Hg—Ag 
                 −1 
               
               
                   
               
            
           
         
       
     
     The third metal that may be present in the metallic glass is a metal which is capable of extending the supercooled liquid region of the metallic glass. 
     Herein, the supercooled liquid region of a metallic glass is a temperature region between a glass transition temperature (“Tg”) and a crystallization temperature (“Tc”) of the metallic glass. In the supercooled liquid region, the metallic glass has relatively low viscosity and shows a liquid-like behavior. The glass transition temperature may be about 50° C. to about 700° C., specifically about 75° C. to 1.0 about 650° C., more specifically about 100° C. to about 600° C. Also, the crystallization temperature may be about 60° C. to about 720° C., specifically about 85° C. to about 670° C., more specifically about 110° C. to about 620° C. 
     The third metal may reduce the glass transition temperature (“Tg”) of the metallic glass and increase the crystallization temperature (“Tc”) of the metallic glass, and thus can extend the supercooled liquid region in which the metallic glass has a liquid-like behavior. The third metal may reduce the Tg of the metallic glass by about 1° C. to about 300° C., specifically about 10° C. to about 250° C., more specifically about 20° C. to about 200° C. Also, the third metal may increase the Tc of the metallic glass by about 1° C. to about 300° C., specifically about 10° C. to about 250° C., more specifically about 20° C. to about 200° C. 
     Thus the supercooled liquid region of the metallic glass is greater with the third metal than without the third metal. 
     While not wanting to be bound by theory, it believed that when the third metal is included in the metallic glass, it hampers interaction of other metal components included therein and thus the metallic glass shows a liquid-like behavior at a lower temperature. Alternatively, when the third metal is included in the metallic glass, it hampers interaction of other metal components and suppresses nucleus formation, and thus delays crystallization and thereby increases the crystallization temperature (“Tc”). 
     In the supercooled liquid region, which is a temperature region between glass transition temperature (Tg) and crystallization temperature (Tc), the metallic glass shows a liquid-like behavior and can wet a lower layer (e.g., lower semiconductor layer) of a solar cell or other electronic device, e.g., semiconductor substrate. Herein, when the supercooled liquid region is extended, the conductive paste may improve wetting properties towards a substrate, such as a semiconductor substrate. 
     For example, when a conductive paste including the metallic glass is applied on a semiconductor substrate to fabricate an electrode for a solar cell, the larger the supercooled liquid region of the softened metallic glass on the semiconductor substrate, the better the conductive paste wets the semiconductor substrate. The improved wetting properties of the conductive paste may allow the conductive powder, which diffuses into the softened metallic glass, to permeate into a larger area of the semiconductor substrate. Accordingly, the electrode disposed on the semiconductor substrate may have better contact (e.g., electrical contact) with the semiconductor substrate, thereby improving adherence therebetween and providing a larger or improved conductive path through which charges produced in the semiconductor substrate by solar light may transport. As a result, the electrode may improve efficiency of a solar cell. 
     The extended supercooled liquid region of the metallic glass may range from about 5° C. to about 200° C., specifically about 10° C. to about 180° C., more specifically about 20° C. to about 160° C., that is having a span of about 5° C. to about 200° C., specifically about 10° C. to about 180° C., more specifically about 20° C. to about 160° C. Thus when the third metal is included in the metallic glass, a supercooled region of the metallic glass may be about 5° C. to about 200° C., specifically about 10° C. to about 180° C., more specifically about 20° C. to about 160° C. Also the supercooled region may be within a temperature range of about 100° C. to about 800° C., specifically about 150° C. to about 750° C., more specifically about 200° C. to about 700° C. 
     The following Table 2 shows that when a metallic glass including copper (Cu) or palladium (Pd), for example as a first metal, zirconium (Zr), as a second metal for example, and aluminum (Al), silver (Ag), nickel (Ni), titanium (Ti), iron (Fe) and/or hafnium (Hf) as a third metal, the metallic glass has a larger supercooled liquid region. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Glass 
                 Crystal- 
                 Supercooled 
               
               
                   
                 transition 
                 lization 
                 liquid 
               
               
                   
                 temperature 
                 temperature 
                 region 
               
               
                   
                 (Tg, K) 
                 (Tc, K) 
                 (ΔTx, K) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Cu 50 Zr 50   
                 675 
                 724 
                 49 
               
               
                 Cu 54 Zr 22 Ni 6 Ti 18   
                 712 
                 769 
                 57 
               
               
                 Cu 48 Zr 48 Al 4   
                 688 
                 756 
                 68 
               
               
                 Cu 47 Zr 47 Al 6   
                 691 
                 770 
                 79 
               
               
                 Cu 50 Zr 43 Al 7   
                 731 
                 792 
                 61 
               
               
                 Cu 46 Zr 46 Al 8   
                 696 
                 789 
                 93 
               
               
                 Cu 45 Zr 45 Al 10   
                 710 
                 787 
                 77 
               
               
                 Cu 45 Zr 45 Ag 10   
                 683 
                 756 
                 73 
               
               
                 Cu 48 Zr 48 Al 2 Ag 2   
                 677 
                 742 
                 65 
               
               
                 Cu 46 Zr 46 Al 4 Ag 4   
                 686 
                 767 
                 81 
               
               
                 Cu 47 Zr 45 Al 4 Ag 4   
                 688 
                 770 
                 82 
               
               
                 Cu 48 Zr 44 Al 4 Ag 4   
                 692 
                 779 
                 87 
               
               
                 Cu 49 Zr 43 Al 4 Ag 4   
                 694 
                 780 
                 86 
               
               
                 Cu 50 Zr 42 Al 4 Ag 4   
                 703 
                 784 
                 81 
               
               
                 Cu 45 Zr 45 Al 5 Ag 5   
                 697 
                 783 
                 86 
               
               
                 Cu 44 Zr 44 Al 6 Ag 6   
                 698 
                 790 
                 92 
               
               
                 Cu 30 Zr 48 Al 8 Ag 8 Ni 6   
                 688 
                 779 
                 91 
               
               
                 Cu 34 Zr 48 Al 8 Ag 8 Ni 2   
                 683 
                 799 
                 116 
               
               
                 Cu 26 Zr 48 Al 8 Ag 8 Ni 10   
                 692 
                 768 
                 76 
               
               
                 Cu 22.8 Zr 61.4 Al 9.9 Ag 1 Fe 4.95   
                 656 
                 753 
                 97 
               
               
                 Cu 34 Zr 48 Al 8 Ag 8 Fe 2   
                 705 
                 806 
                 101 
               
               
                 Cu 36 Zr 46 Al 8 Ag 8 Hf 2   
                 692 
                 794 
                 102 
               
               
                 Cu 36 Zr 42 Al 8 Ag 8 Hf 6   
                 695 
                 796 
                 101 
               
               
                 Cu 34 Zr 48 Al 8 Ag 8 Pd 2   
                 699 
                 794 
                 95 
               
               
                 Cu 30 Zr 48 Al 8 Ag 8 Pd 6   
                 709 
                 796 
                 87 
               
               
                   
               
            
           
         
       
     
     The third metal may be included in an amount of about 10 atomic percent (at %) or less, specifically about 5 at % or less, more specifically about 0.1 to about 10 at %, or about 1 to about 8 at %, based on the total amount of the metallic glass. When it is included within the foregoing range, a metallic glass may include the other components in a sufficient amount and thus have an extended supercooled liquid region and improved solid solubility with the conductive powder, and thus provide sufficient conductivity and oxidation resistance. 
     The fourth metal which may be present in the metallic glass has a higher oxidation property (e.g., standard free energy of formation of oxide) than any other components included in the metallic glass, and thus, may be oxidized before the other components of the metallic glass, thereby preventing their oxidation. The fourth metal may have a standard free energy of formation of oxide at least about 0.1 electron volt (eV), specifically at least about 0.3 eV, more specifically at least about 0.5 eV, or at least about 1 eV greater than a standard free energy of formation of oxide of each of the first, the second, or the third metals. 
     When a conductive paste including the metallic glass is processed in air, it may be exposed to oxygen in the air. If the first metal is oxidized, a conductive paste may have sharply deteriorated conductivity. When the second metal is oxidized, a conductive paste may have decreased solid solubility. When the third metal is oxidized, a metallic glass may have a decreased supercooled liquid region. Thus oxidation of any of the first, the second, or the third metals is undesirable. 
     Accordingly, when a metallic glass includes the fourth metal having a higher oxidation potential than each of the first, the second, and the third metals, the fourth metal is first oxidized and forms a stable oxide layer on the surface of the metallic glass. The oxide layer substantially or effectively prevents oxidation of other components, such as the first, the second, and the third metals therein. Furthermore, degradation of the properties of the conductive paste due to other components in the metallic glass, such as oxides of the first, the second, or the third metals, may be prevented. 
     The fourth metal may have a larger absolute value of a Gibbs Free Energy of metal oxide formation)(ΔG f   0 ) than an absolute value of a Gibbs Free Energy of metal oxide formation of each of the first, the second, and the third metals. The larger the absolute value of the Gibbs free energy of metal oxide formation a metal has, the easier it may be oxidized. The fourth metal may have an absolute value of a Gibbs Free Energy of metal oxide formation of more than about 100 kJ/mol, specifically more than about 120 kJ/mol, more specifically more than about 140 kJ/mol. In an embodiment, the absolute value of the Gibbs Free Energy of metal oxide formation of the fourth metal is about 100 to 2500 kJ/mol, specifically about 120 to about 2300 kJ/mol, more specifically about 140 to about 1900 kJ/mol. 
     The following Table 3 provides Gibbs free energy of metal oxide formation of representative metals. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Metal oxide 
                 Δ f G 0  (kJ/mol) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Cu 2 O 
                 −146 
               
               
                   
                 Ti 2 O 
                 −147.3 
               
               
                   
                 RuO 4   
                 −152.2 
               
               
                   
                 CdO 
                 −228.7 
               
               
                   
                 ZnO 
                 −320.5 
               
               
                   
                 Rh 2 O 3   
                 −343 
               
               
                   
                 K 2 O 2   
                 −425.1 
               
               
                   
                 Na 2 O 2   
                 −447.7 
               
               
                   
                 Ni 2 O 3   
                 −489.5 
               
               
                   
                 Bi 2 O 3   
                 −493.7 
               
               
                   
                 SnO 
                 −515.8 
               
               
                   
                 BaO 
                 −520.3 
               
               
                   
                 GeO 2   
                 −521.4 
               
               
                   
                 Li 2 O 
                 −561.2 
               
               
                   
                 SrO 
                 −561.9 
               
               
                   
                 MgO 
                 −569.3 
               
               
                   
                 BeO 
                 −580.1 
               
               
                   
                 PbO 
                 −601.2 
               
               
                   
                 CaO 
                 603.3 
               
               
                   
                 MoO 3   
                 −668 
               
               
                   
                 WO 3   
                 −764 
               
               
                   
                 Co 3 O 4   
                 −774 
               
               
                   
                 In 2 O 3   
                 −830.7 
               
               
                   
                 SiO 2   
                 −856.3 
               
               
                   
                 TiO 2   
                 −888.8 
               
               
                   
                 Ga 2 O 3   
                 −998.3 
               
               
                   
                 Fe 3 O 4   
                 −1015.4 
               
               
                   
                 ZrO 2   
                 −1042.8 
               
               
                   
                 Cr 2 O 3   
                 −1058.1 
               
               
                   
                 B 2 O 3   
                 −1194.3 
               
               
                   
                 Mn 3 O 4   
                 −1283.2 
               
               
                   
                 Al 2 O 3   
                 −1582.3 
               
               
                   
                 La 2 O 3   
                 −1705.8 
               
               
                   
                 Nd 2 O 3   
                 −1720.8 
               
               
                   
                 Nb 2 O 5   
                 −1766 
               
               
                   
                 V 3 O 5   
                 −1803.3 
               
               
                   
                 Y 2 O 3   
                 −1816.6 
               
               
                   
                 Sc 2 O 3   
                 −1819.4 
               
               
                   
                 Ti 3 O 5   
                 −2317.4 
               
               
                   
                   
               
            
           
         
       
     
     The metallic glass may include an alloy of at least two metals of the first to fourth metals. Thus the at least two of the first to fourth metals that are included in the glass is selected from the first to the fourth metals. Accordingly, the metallic glass may have various combinations of the first to fourth metals. For example, when the first, the second, the third, and the fourth metals are respectively A, B, C, and D, the combination may include alloys of combinations such as A-B-C-D, A-B-C, A-B-D, A-C-D, B-C-D, A-B, A-C, A-D, B-C, B-D, or C-D. 
     In an embodiment, the metallic glass comprises two of the first to the fourth metals. In another embodiment, the metallic glass comprises three of the first to the fourth metals. In another embodiment, the metallic glass comprises each of the first to the fourth metals. In another embodiment, the metallic glass includes at least two of the first to the third metals; the second to the fourth metals; the first, third, and fourth metals; or the first, the second, and the fourth metals. Also, in each embodiment, the first to the fourth metals may be the same or different. Also, a metal of the conductive powder may be the same or different than each of the first to the fourth metals. 
     Herein, the first metal may be included to provide conductivity and may form an alloy with at least one selected from the second metal, the third metal, and the fourth metal. 
     The metallic glass may be at least one selected from, for example, Cu 50 Zr 50 , Cu 54 Zr 22 Ni 6 Ti 18 , Cu 48 Zr 48 Al 4 , Cu 45 Zr 45 Ag 10 , Cu 47 Zr 45 Al 4 Ag 4 , Cu 30 Zr 48 Al 8 Ag 8 Ni 6 , Cu 22.8 Zr 61.4 Al 9.9 Ag 1 Fe 4.95 , Cu 36 Zr 46 Al 8 g 8 Hf 2 , Cu 30 Ag 30 Zr 30 Ti 10 , Ti 50 Ni 15 Cu 32 Sn 3 , Ti 45 Ni 15 Cu 25 Sn 3 Be 7 Zr 5 , Ni 60 Nb 30 Ta 10 , Ni 61 Zr 20 Nb 7 Al 4 Ta 8 , Ni 57.5 Zr 35 Al 7.5 , Zr 41.2 Ti 13.8 Ni 10 Cu 12.5 Be 22.5 , Mg 65 Y 10 Cu 15 Ag 5 Pd 5 , Mn 55 Al 25 Ni 20 , La 55 Al 25 Ni 10 Cu 10 , Mg 65 Cu 7.5 Ni 7.5 Ag 5 Zn 5 Gd 10 , Mg 65 Cu 15 Ag 10 Y 6 Gd 4 , Fe 77 Nb 6 B 17 , Fe 67 Mo 13 B 17 Y 3 , Ca 65 Mg 15 Zn 20 , Ca 66.4 Al 33.6 , Mg 65 CU 15 Ag 10 Gd 10 , Mg 65 CU 15 Ag 10 Gd 10 , Mg 65 CU 25 Gd 10 , Mg 65 Cu 20 Ag 5 Y 10 , Mg 65 Cu 25 Y 10 , Mg 65 Cu 15 Ag 10 Y 10 , Cu 46 Gd 47 Al 7 , Ca 60 Mg 25 Ni 15 , Mg 65 Cu 15 Ag 5 Pd 5 Gd 10 , Mg 70 Ni 10 Gd 20 , Cu 46 Y 42.5 Al 7 , Ti 55 Zr 18 Be 14 Cu 7 Ni 6 , Ti 51 Y 4 Zr 18 Be 14 Cu 7 Ni 6 , Ti 40 Zr 28 Cu 9 Ni 7 Be 16 , Ti 40 Zr 25 Ni 8 Cu 9 Be 18 , Ti 49 Nb 6 Zr 18 Be 14 Cu 7 Ni 6 , Ti 50 Zr 15 Be 18 Cu 9 Ni 8 , Ti 34 Zr 31 Cu 10 Ni 8 Be 17 , Zr 36 Ti 24 Be 40 , Ti 65 Be 18 Cu 9 Ni 8 , Zr 65 Al 7.5 Cu 17.5 Ni 10 , Zr 65 Al 7.5 Cu 12.6 Ni 10 Ag 5 , Cu 50 Zr 40 Ti 10 , Cu 30 Ag 30 Zr 30 Ti 10 , Ni 55 Zr 12 Al 11 Y 22 , and Cu 40 Ni 5 Ag 15 Zr 30 Ti 10 , but is not limited thereto. 
     The organic vehicle may include an organic compound, an optional organic solvent, and optional additives known for use in the manufacture of conductive pastes for solar cells. The organic vehicle is combined with the conductive powder and the metallic glass primarily to provide a viscosity and rheology to the conductive paste effective for printing or coating the conductive paste. A wide variety of inert organic materials can be used, and can be selected by one of ordinary skill in the art without undue experimentation to achieve the desired viscosity and rheology, as well as other properties such as dispersibility of the conductive powder and the metallic glass, stability of conductive powder and the metallic glass and any dispersion thereof, drying rate, firing properties, and the like. Similarly, the relative amounts of the organic compound, any optional organic solvent, and any optional additive can be adjusted by one of ordinary skill in the art without undue experimentation in order to achieve the desired properties of the conductive paste. 
     The organic compound may be a polymer, for example, at least one selected from a C1 to C4 alkyl (meth)acrylate-based resin; a cellulose such as ethyl cellulose or hydroxyethyl cellulose; a phenolic resin; wood rosin; an alcohol resin; a halogenated polyolefin such as tetrafluoroethylene (e.g., TEFLON); and the monobutyl ether of ethylene glycol monoacetate. 
     The organic vehicle may further optionally include at least one additive selected from, for example, a surfactant, a thickener, and a stabilizer. 
     The solvent may be any solvent capable of dissolving or suspending the above other components of the conductive paste and may be, for example, at least one selected from terpineol, butylcarbitol, butylcarbitol acetate, pentanediol, dipentyne, limonene, an ethyleneglycol alkylether, a diethyleneglycol alkylether, an ethyleneglycol alkylether acetate, a diethyleneglycol alkylether acetate, a diethyleneglycol dialkylether acetate, a triethyleneglycol alkylether acetate, a triethylene glycol alkylether, a propyleneglycol alkylether, propyleneglycol phenylether, a dipropyleneglycol alkylether, a tripropyleneglycol alkylether, a propyleneglycol alkylether acetate, a dipropyleneglycol alkylether acetate, a tripropyleneglycol alkyl ether acetate, dimethylphthalic acid, diethylphthalic acid, dibutylphthalic acid, and desalted water. 
     The conductive powder, the metallic glass, and the organic vehicle may be included in an amount of about 30 to about 98 weight percent (wt %), about 1 to about 50 wt %, and about 69 to about 1 wt %, specifically about 40 to about 95 wt %, about 2 to about 40 wt %, and 58 to about 3 wt %, more specifically about 50 to about 90 wt %, about 4 to about 30 wt %, and about 46 to about 6 wt %, respectively, based on the total weight of the conductive paste. 
     The conductive paste is prepared by combining the components of the conductive paste by, for example, mechanical mixing. The conductive paste may be screen-printed to provide an electrode for an electronic device. 
     Hereinafter, illustrated is an electrode fabricated using the aforementioned conductive paste referring to  FIGS. 1 to 4C . 
       FIGS. 1 to 3  are a schematic diagram showing that when a conductive paste according to an embodiment is applied on a semiconductor substrate, a conductive powder and a metallic glass included therein are transformed due to heat and contact with the semiconductor substrate.  FIGS. 4A to 4C  are a schematic diagram enlarging region A of  FIG. 3 . 
     Referring to  FIG. 1 , a conductive paste including a conductive powder  120   a  and a metallic glass  115   a  is applied on a semiconductor substrate  110 . The conductive powder  120   a  and the metallic glass  115   a  may each have the form of a particle having a spherical shape, for example. 
     Referring to  FIG. 2 , when the metallic glass  115   a  is heated to a first temperature higher than its glass transition temperature (“Tg”), the metallic glass  115   a  becomes soft and turns into a liquid-like metallic glass  115   b . The first temperature may be about 1 to about 300° C., specifically about 5 to about 250° C., more specifically about 10 to about 200° C. higher than the Tg of the metallic glass. The liquid-like metallic glass  115   b , which has a liquid-like properties, may fill a gap among a plurality of particles of the conductive powder  120   a . Herein, the metallic glass  115   a  is first softened, because the glass transition temperature (“Tg”) of the metallic glass  115   a  is lower than the sintering temperature (“Ts”) of the conductive powder  120   a.    
     Referring to  FIG. 3 , when a conductive paste is heated to a second temperature higher than the sintering temperature, the conductive powder  120   a  is sintered and particles of the conductive powder  120   a  closely bond with neighboring particles of conductive powder  120   a  to form a conductive powder agglomerate  120   b . The second temperature may be about 1 to about 300° C., specifically about 5 to about 250° C., more specifically about 10 to about 200° C. higher than the Ts of the metallic glass. 
     As shown in  FIGS. 2 and 3 , the liquid-like metallic glass, which has liquid-like properties, is a supercooled liquid and wets a semiconductor substrate  110 . 
     Referring to  FIG. 4A , when the liquid-like metallic glass  115   b  is a supercooled liquid, some conductive particles  120   c  of the conductive powder agglomerate  120   b  diffuse into the liquid-like metallic glass  115   b . As aforementioned, the liquid-like metallic glass  115   b  includes a component which can form a solid solution with the conductive powder agglomerate  120   b.    
     In addition, as aforementioned, when a metallic glass has an extended supercooled liquid region, the liquid-like metallic glass  115   b  has a low viscosity and remains on and wets the semiconductor substrate  110 . Accordingly, contact between the liquid-like metallic glass  115   b  and the semiconductor substrate  110  is improved. 
     Referring to  FIG. 4B , when heated to a third temperature higher than the second temperature, conductive particles  120   c  diffuse into the liquid-like metallic glass  115   b  and permeate into the semiconductor substrate  110 . The third temperature may be about 1 to about 300° C., specifically about 5 to about 250° C., more specifically about 10 to about 200° C. higher than the second temperature. Herein, as aforementioned, the liquid-like metallic glass  115   b  may have improved wetting properties and provide improved contact with the semiconductor substrate  110 . Accordingly, the metallic glass may have a larger area in which conductive particles 120 c  permeate into the semiconductor substrate  110 . 
     Referring to  FIG. 4C , when the semiconductor substrate  110  is cooled down, conductive particles  120   c  permeated into the semiconductor substrate  110  crystallize to form crystallized conductive particles  120   d  at the surface of the semiconductor substrate  110 . Also, the liquid-like metallic glass  115   b  may also crystallize to form a crystalline metallic glass  115   c  and the conductive particles  120   c  in the metallic glass may also crystallize. 
     In this way, the conductive powder agglomerate  120   b  may be made into an electrode  120 . Also, a buffer layer  115  including the crystalline metallic glass  115   c  may be formed between the electrode  120  and the semiconductor substrate  110 . 
     The crystallized conductive particles  120   d  in the buffer layer  115  and at the surface of the semiconductor substrate  110  effectively improve transfer of charges produced by solar light in the semiconductor substrate  110  to the electrode  120  and, simultaneously, decrease a contact resistance between the semiconductor substrate  110  and the electrode  120 , thereby decreasing charge loss of a solar cell. Ultimately, the solar cell may have improved efficiency. 
     The electrode may be used as a conductive electrode for various other electronic devices. 
     A representative electronic device is a solar cell. 
     Referring to  FIG. 5 , a solar cell according to an embodiment is disclosed in further detail. 
       FIG. 5  is a cross-sectional view showing a solar cell according to an embodiment. 
     In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like elements throughout the specification. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
     Hereinafter, positions of (or spatial relationships between) components will be described with respect to a semiconductor substrate  110  for better understanding and ease of description, but the disclosed embodiment is not limited thereto. In addition, for clarity of description, a solar energy incident side of a semiconductor substrate  110  is called a front side, and the opposite side is called a rear side, although alternative configurations are possible. 
     Referring to  FIG. 5 , a solar cell according to an embodiment may include a semiconductor substrate  110  including a lower semiconductor layer  110   a  and an upper semiconductor layer  110   b.    
     The semiconductor substrate  110  may comprise a crystalline silicon or a compound semiconductor. The crystalline silicon may be, for example, a silicon wafer. One of the lower semiconductor layer  110   a  and the upper semiconductor layer  110   b  may be a semiconductor layer doped with a p-type impurity, and the other may be a semiconductor layer doped with an n-type impurity. For example, the lower semiconductor layer  110   a  may be a semiconductor layer doped with a p-type impurity, and the upper semiconductor layer  110   b  may be a semiconductor layer doped with an n-type impurity. Herein, the p-type impurity may be a Group III element such as boron (B), and the n-type impurity may be a Group V element such as phosphorus (P). 
     The surface of the upper semiconductor layer  110   b  may be textured, for example by surface texturing. The surface-textured upper semiconductor layer  110   b  may have protrusions and depressions, and may comprise a pyramidal shape, or may have a porous structure having a honeycomb shape, for example. The surface-textured upper semiconductor layer  110   b  may have an enhanced surface area to improve the light-absorption rate and decrease reflectivity, thereby improving efficiency of a solar cell. 
     A front electrode  120  is disposed (e.g., formed) on the upper semiconductor layer  110   b . The front electrode  120  may be arranged in parallel to a direction of the substrate, and may have a grid pattern shape to reduce shadowing loss and sheet resistance. 
     The front electrode  120  may comprise a conductive material, for example a low resistivity conductive material such as silver (Ag). 
     The front electrode  120  may be disposed by a screen printing a conductive paste. The conductive paste is the same as described above. 
     A buffer layer  115  is disposed between the upper semiconductor layer  110   b  and the front electrode  120  by heat treating the conductive paste disposed to form the front electrode  120 . The buffer layer  115  may be conductive due to inclusion of the metallic glass. Because the buffer layer  115  has portions that contact the electrode  120  and the upper semiconductor layer  110   b , it may decrease loss of electric charges by enlarging the effective path for transferring electric charges between the upper semiconductor layer  110   b  and the front electrode  120 . The buffer layer may also reduce resistive losses, for example. 
     The metallic glass of the buffer layer  115  is derived from the conductive paste used to form the front electrode  120 . The metallic glass may melt before the conductive material of the front electrode  120  during processing, so that the metallic glass is disposed under the front electrode  120  to form the buffer layer. 
     A bus bar electrode (not shown) may be disposed on the front electrode  120 . The bus bar electrode can connect adjacent solar cells of a plurality of solar cells. 
     A dielectric layer  130  may be formed under the semiconductor substrate  110 . The dielectric layer  130  may increase efficiency of a solar cell by substantially or effectively preventing recombination of electric charges and leaking of electric current. The dielectric layer  130  may include a penetration part  135  (e.g., a through hole), and the semiconductor substrate  110  and a rear electrode  140  that will be further described below may contact through the penetration part  135 . 
     The dielectric layer  130  may comprise at least one selected from silicon oxide (SiO 2 ), silicon nitride (SiN x ), aluminum oxide (Al 2 O 3 , and may have a thickness of about 100 to about 2000 angstroms (Å), specifically about 200 to about 1800 Å, more specifically about 300 to about 1600 Å. 
     A rear electrode  140  is disposed under the dielectric layer  130 . The rear electrode  140  may comprise a conductive material, and the conductive material may be an opaque metal such as aluminum (Al). The rear electrode  140  may be disposed by screen printing a conductive paste in the same manner as the front electrode  120 . 
     In an embodiment, a buffer layer  115  is disposed between the rear electrode  140  and the lower semiconductor layer  110   a  in the same manner as the front electrode  120 . In another embodiment, the buffer layer is disposed between the rear electrode  140  and the lower semiconductor layer  110   a  or between the front electrode  120  and the upper semiconductor layer  110   b.    
     Hereinafter, a method of manufacturing the solar cell is further described with reference to  FIG. 5 . 
     First, a semiconductor substrate  110 , such as a silicon wafer, is prepared. The semiconductor substrate  110  may be doped with an impurity, such as a p-type impurity, as an example. 
     Then the semiconductor substrate  110  may be subjected to a surface texturing treatment. The surface-texturing treatment may be performed by a wet method using at least one strong acid selected from, for example, nitric acid, hydrofluoric acid, and the like, or at least one strong base selected from, for example, sodium hydroxide and the like; or the surface-texturing treatment may be performed by a dry method such as plasma treatment. 
     Then, the semiconductor substrate  110  may be doped with an n-type impurity, for example. The n-type impurity may be doped by diffusing at least one selected from, for example, POCl 3 , H 3 PO 4 , and the like at a high temperature. The semiconductor substrate  110  includes a lower semiconductor layer  110   a  and an upper semiconductor layer  110   b  doped with different impurities than each other. 
     Then a conductive paste for a front electrode is applied on the upper semiconductor layer  110   b . The conductive paste for a front electrode may be applied by a screen printing method. The screen printing method includes applying the conductive paste, which comprises a conductive powder, a metallic glass, and an organic vehicle at a location where a front electrode is disposed, and drying the same. 
     As further disclosed above, the conductive paste may include a metallic glass, and the metallic glass may be prepared using any suitable method such as melt spinning, infiltration casting, gas atomization, ion irradiation, or mechanical alloying. 
     Then the conductive paste for a front electrode may be dried. 
     A dielectric layer  130  may be provided by disposing (e.g., stacking, forming, or depositing) aluminum oxide (Al 2 O 3 ) or silicon oxide (SiO 2 ) on an entirety of or on a portion of a rear side of the semiconductor substrate  110 . The dielectric layer  130  may be disposed by a plasma enhanced chemical vapor deposition (“PECVD”) method, for example. 
     Then a penetration part  135  may be provided on a portion of the dielectric layer  130  by ablation with a laser, for example. 
     The conductive paste for a rear electrode is subsequently applied on a side of the dielectric layer  130 , which in an embodiment is opposite the semiconductor substrate  110 , by a screen printing method. 
     Then, a conductive paste for a rear electrode is dried. 
     Next, the conductive paste for a front electrode and the conductive paste for a rear electrode are co-fired (e.g., heat treated), or fired individually. Thus the conductive paste for a front electrode and the conductive paste for a rear electrode may be fired in the same or in different processes. 
     The firing may be performed in a furnace and at a temperature higher than the melting temperature of the conductive metal, for example at a temperature ranging from about 400° C. to about 1000° C., specifically about 450° C. to about 950° C., more specifically about 500° C. to about 900° C. 
     Hereinafter, a solar cell according to another embodiment is disclosed referring to  FIG. 6 . 
       FIG. 6  is a cross-sectional view showing a solar cell according to another embodiment. 
     A solar cell may include a semiconductor substrate  110  doped with a p-type or an n-type impurity. The semiconductor substrate  110  may include a first doping region  111   a  and second doping region  111   b  that are provided on the rear side of the semiconductor substrate  110 , and are doped with different impurities than each other. For example, the first doping region  111   a  may be doped with an n-type impurity, and the second doping region  111   b  may be doped with a p-type impurity. The first doping region  111   a  and the second doping region  111   b  may be alternately disposed on the rear side of the semiconductor substrate  110 . 
     The front side of the semiconductor substrate  110  may be surface-textured, and therefore may enhance the light-absorption rate and decrease the reflectivity of the solar cell, thereby improving efficiency of the solar cell. An insulation layer  112  is provided on the semiconductor substrate  110 . The insulation layer  112  may comprise an insulating material that is substantially transparent and thus absorbs little light, for example at least one selected from silicon nitride (SiN x ), silicon oxide (SiO 2 ), titanium oxide (TiO 2 ), aluminum oxide (Al 2 O 3 ), magnesium oxide (MgO), and cerium oxide (CeO 2 ). The insulation layer  112  may be a single layer or more than one layer. The insulation layer  112  may have a thickness ranging from about 200 to about 1500 Å, specifically 300 to about 1400 Å, more specifically about 400 to about 1300 Å. 
     The insulation layer  112  may be an anti-reflective coating (“ARC”) that decreases the reflectivity of light and increases selectivity of a particular wavelength region on the surface of the solar cell, and simultaneously improves properties of silicon on the surface of the semiconductor substrate  110 , thereby increasing efficiency of the solar cell. 
     A dielectric layer  150  including first and second penetration parts may be disposed on the rear side of the semiconductor substrate  110 . 
     The front electrode  120  electrically connected with the first doping region  111   a  and the rear electrode  140  electrically connected with the second doping region  111   b  are disposed on the rear side of the semiconductor substrate  110 , respectively. The front electrode  120  and the first doping region  111   a  may be contacted through the first penetration part, and the rear electrode  140  and the second doping region  111   b  may be in contact through the second penetration part. The front electrode  120  and the rear electrode  140  may be alternately disposed. 
     As disclosed in the above embodiment, the front electrode  120  and the rear electrode  140  may be disposed using a conductive paste including a conductive powder, a metallic glass, and an organic vehicle, which is the same as described above. 
     A buffer layer  115  is disposed between the first doping region  111   a  and the front electrode  120 , or between the second doping region  111   b  and the rear electrode  140 . The buffer layer  115  may be electrically conductive due inclusion of a metallic glass. Because the buffer layer  115  includes portions contacting either the front electrode  120  or the rear electrode  140 , and portions contacting either the first doping region  111   a  or the second doping region  111   b , respectively, loss of electric charge may be decreased by enlarging or otherwise improving the path for transferring electric charge between the first doping region  111   a  and the front electrode  120 , or between the second doping region  111   b  and the rear electrode  140 . In addition, the buffer layer  115  may substantially or effectively prevent a material of the front electrode  120  or the rear electrode  140  from diffusing into the first or second doping regions  111   a  or  111   b , respectively. 
     A solar cell according to the embodiment including both of the front electrode  120  and the rear electrode  140  on the rear surface of the solar cell may decrease an area where a metal is disposed on the front surface. This may decrease shadowing loss and increase solar cell efficiency. 
     Hereinafter, the method of manufacturing a solar cell will be further disclosed referring to  FIG. 6 . 
     First, a semiconductor substrate  110  doped with, for example, an n-type impurity is prepared. Then, the semiconductor substrate  110  is surface-textured, and insulation layer  112  and dielectric layer  150  are disposed on a front side and a rear side of the semiconductor substrate  110 , respectively. The insulation layer  112  and the dielectric layer  150  may be provided by chemical vapor deposition (“CVD”), for example. 
     Then, the first doping region  111   a  and the second doping region  111   b  may be disposed by sequentially doping a p-type impurity and an n-type impurity at a high concentration in the rear side of the semiconductor substrate  110 . 
     Then, a conductive paste for a front electrode is applied on a portion (e.g. on a side) of the dielectric layer  150  corresponding to the first doping region  111   a , and a conductive paste for a rear electrode is applied a portion of the dielectric layer  150  corresponding to the second doping region  111   b . The conductive paste for the front electrode and the conductive paste for the rear electrode may be disposed by screen printing, for example, and the conductive paste may comprise a conductive powder, a metallic glass, and an organic vehicle. 
     Next, the conductive paste for the front electrode and the conductive paste for the rear electrode may be fired together or separately. The firing (e.g., heat treating) may be performed in a furnace at a temperature higher than the melting temperature of a conductive metal. 
     Herein, the conductive paste is applied to provide an electrode for a solar cell, but the conductive paste may also be used to provide an electrode for various other electronic devices such as a plasma display panel (“POP”), a liquid crystal display (“LCD”), or an organic light emitting diode (“OLED”). 
     While this disclosure has been described in connection with what is presently considered to be practical 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.