Patent Publication Number: US-9893221-B2

Title: Solar cell and method of fabricating the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/262,441, filed Sep. 30, 2011, which is the U.S. national stage application of International Patent Application No. PCT/KR2010/001989, filed Mar. 31, 2010, which claims priority to Korean Application Nos. 10-2009-0027874, filed Mar. 31, 2009, and 10-2009-0027875, filed Mar. 31, 2009, the disclosures of each of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to a solar cell and a method of fabricating the same. 
     BACKGROUND ART 
     Recently, as energy consumption has been increased, a solar cell capable of converting solar energy into electric energy has been developed. 
     In particular, a CIGS solar cell, which is a PN hetero junction device having a substrate structure including a glass substrate, a metal back electrode layer, a P type CIGS light absorption layer, a high-resistance buffer layer, and an N type window layer, is extensively used. 
     In addition, in order to fabricate such a solar cell, a mechanical patterning process may be performed. However, if the mechanical patterning is performed, the precision degree may be lowered and the defect may occur during the patterning process. 
     DISCLOSURE OF THE INVENTION 
     Technical Problem 
     The disclosure provides a solar cell and a method of fabricating the same, in which cells can be efficiently connected with each other through the precise patterning, a light absorption layer may have a wide surface area, and the efficiency of the solar cell can be improved. 
     The disclosure provides a solar cell and a method of fabricating the same, in which coupling strength between a substrate and a back electrode can be reinforced and the leakage current can be minimized. 
     Technical Solution 
     A solar cell according to the embodiment includes a plurality of back electrode patterns spaced apart from each other on a substrate; a light absorption layer including contact patterns to connect electrodes to each other and division patterns to divide cells into unit cells on the substrate formed with the back electrode patterns; top electrode patterns spaced apart from each other by the division patterns on the light absorption layer; and insulating patterns among the back electrode patterns or on the back electrode patterns, wherein the top electrode patterns are filled in the contact patterns and electrically connected to the back electrode patterns. 
     A method of fabricating a solar cell according to the embodiment includes forming a plurality of back electrode patterns spaced apart from each other on a substrate and forming insulating patterns among the back electrode patterns or on the back electrode patterns; forming a light absorption layer including contact patterns to connect electrodes to each other and division patterns to divide cells into unit cells on the substrate formed with the back electrode patterns; and forming top electrode patterns spaced apart from each other by the division patterns on the light absorption layer, wherein the top electrode patterns are filled in the contact patterns and electrically connected to the back electrode patterns. 
     Advantageous Effects 
     According to the solar cell and the method of fabricating the same of the first and second embodiments, first insulating patterns are formed on back electrode patterns, so that lower back electrode patterns can be prevented from being damaged. 
     In addition, the back electrode patterns are not exposed to the outside due to the first insulating patterns after the division patterns have been formed, so that the back electrode patterns can be prevented from being oxidized and can be protected from impurities. 
     In addition, since the cells are divided by a laser, a distance between adjacent cells can be reduced, a process can be simplified, and an area of a light incident region can be widened. 
     Further, the damage caused by the mechanical stress can be reduced, so that the efficiency of the solar cell can be improved. 
     According to the solar cell and the method of fabricating the same of the third embodiment, second insulating patterns are formed among the back electrode patterns, so that coupling strength between the back electrode patterns and the second insulating patterns can be reinforced. 
     That is, since the coupling strength between the back electrode patterns and the second insulating patterns can be reinforced, the back electrode patterns can be prevented from being delaminated from the substrate. 
     When the patterning process is performed by using a laser to form the back electrode patterns, an edge region of the back electrode patterns may be delaminated or peeled off. However, according to the embodiment, the back electrode patterns can be formed without using the laser, so that the back electrode patterns can be prevented from being deformed by the laser patterning. 
     In addition, since the back electrode patterns may not be delaminated, the light absorption layer can be stably formed, so that the quality and efficiency of the solar cell can be improved. 
     Further, since the second insulating patterns are formed among the back electrode patterns, the leakage current can be prevented from occurring among the back electrode patterns. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 to 10  are sectional views showing a method of fabricating a solar cell according to the first embodiment; 
         FIGS. 11 to 14  are sectional views showing a method of fabricating a solar cell according to the second embodiment; and 
         FIGS. 15 to 23  are sectional views showing a method of fabricating a solar cell according to the third embodiment. 
     
    
    
     MODE FOR INVENTION 
     In the description of the embodiments, it will be understood that, when a substrate, a film, an electrode, a groove or a layer is referred to as being “on” or “under” another substrate, another film, another electrode, another groove, or another layer, it can be “directly” or “indirectly” over the other substrate, film, electrode, groove, or layer, or one or more intervening layers may also be present. Such a position of the layer has been described with reference to the drawings. The thickness and size of each layer shown in the drawings may be exaggerated, omitted or schematically drawn for the purpose of convenience or clarity. In addition, the size of elements does not utterly reflect an actual size. 
       FIGS. 1 to 10  are sectional views showing a method of fabricating a solar cell according to the first embodiment. 
     As shown in  FIG. 1 , a back electrode  201  is formed on a substrate  100 . The substrate  100  includes a glass substrate, a ceramic substrate, such as an alumina substrate, a stainless steel substrate, a titanium substrate or a polymer substrate. 
     The glass substrate may include soda lime glass and the polymer substrate may include polyimide. 
     The substrate  100  may be rigid or flexible. 
     The back electrode  201  may include a conductor such as a metal. 
     For instance, the back electrode  201  can be formed through a sputtering process by using a molybdenum (Mo) target. 
     The molybdenum (Mo) has high electric conductivity, superior ohmic contact property with respect to a light absorption layer and high temperature stability in the Se atmosphere. 
     In addition, although not shown in the drawings, the back electrode  201  may include at least one layer. 
     If the back electrode  201  includes a plurality of layers, the layers may be formed by using different materials. 
     In addition, as shown in  FIG. 2 , a plurality of first insulating patterns  10  are formed on the back electrode  201 . 
     In order to form the first insulating patterns  10 , an insulating layer is formed on the back electrode  201  and a patterning process is performed with respect to the insulating layer. 
     The insulating layer can be formed through one of a sputtering process, a thermal deposition process, a spray process and a spin coating process. 
     The patterning process to form the first insulating patterns  10  may include a photolithography process such as a wet etching process or a dry etching process. 
     The first insulating patterns  10  may include an insulating material or a polymer compound, which does not react with the back electrode  201  and the light absorption layer to be formed later. 
     For instance, the first insulating patterns  10  may include one of SiO x  (x=2 to 4), SiN x  (x=4), PMMA (polymethyl methacrylate), polyimide, and polypropylene. 
     The first insulating patterns  10  are disposed among the cells to divide the cells from each other. 
     That is, each insulating pattern  10  is disposed between two adjacent cells by taking the position of the light absorption layer and the top electrode, which will be formed later, into consideration. 
     Then, as shown in  FIG. 3 , the patterning process is performed with respect to the back electrode  201  to form back electrode patterns  200 . 
     The back electrode patterns  200  are aligned such that the substrate  100  can be exposed through the first insulating patterns  10 . 
     In addition, the back electrode patterns  200  can be aligned in the form of a stripe or a matrix corresponding to the cells. 
     However, the back electrode patterns  200  may not be limited to the above shape, but may have various shapes. 
     After that, as shown in  FIG. 4 , the light absorption layer  300 , the first buffer layer  400  and the second buffer layer  500  are formed on the back electrode  201 . 
     The light absorption layer  300  includes the Ib-IIIb-VIb group compound. 
     In detail, the light absorption layer  300  may include the Cu—In—Ga—Se (Cu(In,Ga)Se 2 ; CIGS) compound. 
     In contrast, the light absorption layer  300  may include the Cu—In—Se (CuInSe 2 ; CIS) compound or the Cu—Ga—Se (CuGaSe 2 ; CGS) compound. 
     For instance, in order to form the light absorption layer  300 , a CIG metal precursor layer is formed on the back electrode  201  by using a Cu target, an In target or a Ga target. 
     The metal precursor layer reacts with Se through the selenization process, thereby forming the CIGS light absorption layer  300 . 
     In addition, while the process for forming the metal precursor layer and the selenization process are being performed, alkali components contained in the substrate  100  are diffused into the metal precursor layer and the light absorption layer  300  through the back electrode patterns  200 . 
     The alkali components may improve the grain size of the light absorption layer  300  and the crystal property. 
     The light absorption layer  300  receives the incident light to convert the incident light into the electric energy. The light absorption layer  300  generates the photo-electromotive force based on the photoelectric effect. 
     The first buffer layer  400  can be formed by depositing CdS on the light absorption layer  300 . 
     The first buffer layer  400  is an N type semiconductor layer and the light absorption layer  300  is a P type semiconductor layer. Thus, the light absorption layer  300  and the first buffer layer  400  may form the PN junction. 
     In addition, the second buffer layer  500  may be prepared as a transparent electrode layer including one of ITO, ZnO and i-ZnO. 
     The first and second buffer layers  400  and  500  are disposed between the light absorption layer  300  and the top electrode to be formed later. 
     Since there is great difference in the lattice constant and the energy bandgap between the light absorption layer  300  and the top electrode, if the first and second buffer layers  400  and  500  having the intermediate bandgap are interposed between the light absorption layer  300  and the top electrode, the superior junction can be obtained. 
     According to the present embodiment, two buffer layers are formed on the light absorption layer  300 . However, the embodiment is not limited thereto. For instance, only one buffer layer can be formed on the light absorption layer  300 . 
     Then, as shown in  FIG. 5 , contact patterns  310  are formed through the light absorption layer  300 , the first buffer layer  400  and the second buffer layer  500 . 
     The contact patterns  310  can be formed through laser irradiation and the back electrode patterns  200  are partially exposed through the contact patterns  310 . 
     At this time, the laser beam irradiated onto the second buffer layer  500  may have a wavelength different from a wavelength of the laser beam irradiated onto the light absorption layer  300  and the first buffer layer  400 . In addition, the intensity of the laser beam can be adjusted through a lens. 
     Since the second buffer layer  500  has a high energy bandgap, a laser beam having relatively high output power is used for the second buffer layer  500 . In addition, since the first buffer layer  400  and the light absorption layer  300  has a low energy bandgap, a laser beam having relatively low output power is used for the first buffer layer  400  and the light absorption layer  300  to form the contact patterns  310 . 
     Then, as shown in  FIG. 6 , a transparent conductive material is deposited on the second buffer layer  500  to form a top electrode and a connection wire  700 . 
     When the transparent conductive material is deposited on the second buffer layer  500 , the transparent conductive material is filled in the contact patterns  310  to form the connection wire  700 . 
     The back electrode patterns  200  are electrically connected to the top electrode  600  through the connection wire  700 . 
     In order to form the top electrode  600 , the sputtering process is performed with respect to the second buffer layer  500  by using aluminum-doped ZnO or alumina-doped ZnO. 
     The top electrode  600  is a window layer forming the PN junction with respect to the light absorption layer  300 . Since the top electrode  600  serves as a transparent electrode for the solar cell, the top electrode  600  is formed by using ZnO having high light transmittance and superior electric conductivity. 
     In addition, ZnO is doped with aluminum or alumina, so that the top electrode  600  has a low resistance value. 
     In order to form the top electrode  600 , a ZnO layer is deposited through the RF sputtering process using a ZnO target, the reactive sputtering using a Zn target, or the metal organic chemical vapor deposition (MOCVD). 
     In addition, a dual structure can be formed by depositing an ITO (indium tin oxide) layer having the superior electro-optical characteristic onto the ZnO layer. 
     Then as shown in  FIG. 7 , division patterns  320  are formed through the light absorption layer  300 , the first buffer layer  400  and the second buffer layer  500 . 
     The division patterns  320  can be formed through the laser irradiation such that the top surface of the first insulating patterns  10  can be exposed through the division patterns  320 . 
     The laser beam used to form the division patterns  320  has a wavelength of about 532 nm to about 1064 nm and power of about 5 W to about 20 W. 
     The first buffer layer  400 , the second buffer layer  500  and the top electrode  600  are separated from each other by the division patterns  320 . In addition, the cells C 1  and C 2  are separated from each other by the first insulating patterns  10  and the division patterns  320 . 
     Since the first insulating patterns  10  are formed on the back electrode patterns  200 , the lower back electrode patterns  200  can be prevented from being damaged when the laser patterning process is performed. 
     In addition, since the back electrode patterns  200  are not exposed to the outside due to the first insulating patterns  10  after the division patterns  320  has been formed, the back electrode patterns  200  can be prevented from being oxidized and can be protected from the impurities. 
     When the division patterns  320  are formed, the over etching is performed to electrically separate adjacent cells from each other, so the first insulating patterns  10  may be partially removed. 
     However, the first insulating patterns  10  may not be completely removed and the back electrode patterns  200  are not exposed. 
     According to the present embodiment, a width of the division patterns  320  is equal to a width of the first insulating patterns  10 , but the embodiment is not limited thereto. For instance, the width of the division patterns  320  may be smaller than the width of the first insulating patterns  10 . 
     That is, as shown in  FIG. 8 , the division patterns  320  have a width sufficient for dividing the cells C 1  and C 2  from each other, and the width of the first insulating patterns  10  may be larger than the width of the division patterns  320 . 
     In addition, as shown in  FIG. 9 , the width of the division patterns  320  may be larger than the width of the first insulating patterns  10 . 
     The first buffer layer  400 , the second buffer layer  500 , and the light absorption layer  300  may be aligned in the form of a stripe or a matrix by the division patterns  320 . 
     However, the division patterns  320  may not be limited to the above shape, but may have various shapes. 
     The cells C 1  and C 2  including the back electrode patterns  200 , the light absorption layer  300 , the first buffer layer  400 , the second buffer layer  500  and the top electrode  600  are formed by the division patterns  320 . The cell C 1  can be connected to the cell C 2  by the connection wire  700 . That is, the connection wire  700  electrically connects the back electrode patterns  200  of the second cell C 2  with the top electrode  600  of the first cell C 1  adjacent to the second cell C 2 . 
     After that, as shown in  FIG. 10 , a transparent resin  800  and a top substrate  900  are formed on the top electrode  600 . 
     The transparent resin  800  can be formed by performing the thermal process using EVA (ethylene vinyl acetate copolymer), and the top substrate  900  can be formed by using heat strengthened glass. The transparent resin  800  is filled in the division patterns  320  so that the stack structure of the first insulating patterns  10  and the transparent resin  800  can be formed on the division patterns  320 . 
       FIGS. 11 to 14  are sectional views showing a method of fabricating a solar cell according to the second embodiment. In the following description of the second embodiment, the elements and structures the same as those of the first embodiment will be depicted with the same reference numerals and detailed description thereof will be omitted in order to avoid redundancy. 
     As shown in  FIG. 11 , a back electrode  201  is formed on a substrate  100 . 
     The substrate  100  includes a glass substrate, a ceramic substrate, such as an alumina substrate, a stainless steel substrate, a titanium substrate or a polymer substrate. 
     The back electrode  201  may include a conductor such as a metal. 
     Although not shown in the drawings, the back electrode  201  may include at least one layer. 
     In addition, as shown in  FIG. 12 , a patterning process is performed with respect to the back electrode  201  to form back electrode patterns  200 . 
     The back electrode patterns  200  may expose the substrate  100 . 
     The back electrode patterns  200  can be aligned in the form of a stripe or a matrix corresponding to the cells. 
     Then, as shown in  FIG. 13 , an insulating layer  5  is formed on the substrate  100  having the back electrode patterns  200 . 
     The insulating layer  5  can be formed through one of a sputtering process, a thermal deposition process, a spray process and a spin coating process. 
     The insulating layer  5  may include an insulating material or a polymer compound, which does not react with the back electrode  201  and the light absorption layer to be formed later. 
     For instance, the insulating layer  5  may include one of SiO x  (x=2 to 4), SiN x  (x=4), PMMA (polymethyl methacrylate), polyimide, and polypropylene. 
     After that, as shown in  FIG. 14 , a plurality of first insulating patterns  10  are formed on the back electrode patterns  200 . 
     The first insulating patterns  10  may be formed by performing a photolithography process such as a wet etching process or a dry etching process with respect to the insulating layer  5  formed on the back electrode patterns  200 . 
     The first insulating patterns  10  can be disposed among the cells to divide the cells from each other. 
     That is, each insulating pattern  10  is disposed between two adjacent cells by taking the position of the light absorption layer and the top electrode, which will be formed later, into consideration. 
     The process to form the light absorption layer  300  and the top electrode  600  on the first insulating patterns  10  is identical to the process shown in  FIGS. 4 to 10 , so the detailed description thereof will be omitted in order to avoid redundancy. 
     According to the solar cell and the method of fabricating the same of the first and second embodiments, the first insulating patterns are formed on the back electrode patterns, so the lower back electrode patterns can be prevented from being damaged when the laser patterning process is performed to divide the cells. 
     In addition, the back electrode patterns are not exposed to the outside due to the first insulating patterns after the division patterns have been formed, so that the back electrode patterns can be prevented from being oxidized and can be protected from impurities. 
     Further, since the cells are divided by a laser, a distance between adjacent cells can be reduced, a process can be simplified, and an area of a light incident region can be widened. 
     In addition, the damage caused by the mechanical stress can be reduced, so that the efficiency of the solar cell can be improved. 
       FIGS. 15 to 22  are sectional views showing a method of fabricating a solar cell according to the third embodiment. 
     As shown in  FIG. 15 , second insulating patterns  110  are formed on a substrate  100 . The substrate  100  includes a glass substrate, a ceramic substrate, such as an alumina substrate, a stainless steel substrate, a titanium substrate or a polymer substrate. 
     The glass substrate may include soda lime glass. 
     The substrate  100  may be rigid or flexible. 
     In order to form the second insulating patterns  110 , an insulating layer (not shown) is formed on the substrate  100  and the patterning process is performed with respect to the insulating layer. The substrate  100  can be exposed through the second insulating patterns  110 . 
     The insulating layer may be formed by using photoresist. In detail, the photolithography process is performed with respect to the photoresist to form the second insulating patterns  110 . 
     The second insulating patterns  110  can be formed through various methods. For instance, the photoresist or the insulating material can be formed on the substrate  100  through the screen printing scheme, the inkjet printing scheme or the gravure printing scheme. 
     In addition, the photolithography process can be directly performed with respect to the substrate  100  to partially remove the substrate  100 , thereby forming the second insulating patterns  110 . 
     The second insulating patterns  110  are formed by using the material the same as that of the substrate  100 . In detail, the second insulating patterns  110  may include the photoresist or the insulating material. 
     The second insulating patterns  110  are aligned among the back electrode patterns by taking the position of the back electrode patterns into consideration. 
     Then, as shown in  FIG. 16 , the back electrode layer  201  is formed on the substrate  100  having the second insulating patterns  110 . 
     The back electrode layer  201  may include a conductor such as a metal. 
     For instance, the back electrode layer  201  can be formed through a sputtering process by using a molybdenum (Mo) target. 
     The molybdenum (Mo) has high electric conductivity, superior ohmic contact property with respect to a light absorption layer and high temperature stability in the Se atmosphere. 
     In addition, although not shown in the drawings, the back electrode layer  201  may include at least one layer. 
     If the back electrode layer  201  includes a plurality of layers, the layers may be formed by using different materials. 
     After that, as shown in  FIG. 17 , the back electrode patterns  200  are formed among the second insulating patterns  110  on the substrate  100 . 
     The back electrode patterns  200  can be formed by partially removing the back electrode layer  201  such that the second insulating patterns  110  can be exposed. 
     At this time, the back electrode layer  201  can be partially removed through one of the chemical mechanical polishing (CMP) process, the wet etching process, the dry etching process and the sand blast process. 
     The height of the second insulating patterns  110  is equal to the height of the back electrode patterns  200 . 
     That is, the top surface of the second insulating patterns  110  is aligned on the same plane with the top surface of the back electrode patterns  200 . 
     However, the height of the second insulating patterns  110  and the back electrode patterns  200  may not be limited to the above. For instance, the height of the back electrode patterns  200  may be lower than the height of the second insulating patterns  110 . 
     In detail, when the back electrode layer  201  is partially removed to expose the second insulating patterns  110 , the back electrode layer  201  is over-etched such that the height of the back electrode patterns  200  may be lower than the height of the second insulating patterns  110 . 
     Since the second insulating patterns  110  are aligned among the back electrode patterns  200 , the coupling strength between the back electrode patterns  200  and the second insulating patterns  110  can be reinforced. 
     That is, since the coupling strength between the back electrode patterns  200  and the second insulating patterns  110  can be reinforced, the back electrode patterns  200  can be prevented from being delaminated from the substrate  100 . 
     In addition, the second insulating patterns  110  may have a width smaller than a width of the back electrode patterns  200 . 
     In addition, the back electrode patterns  200  may be aligned in the form of a stripe or a matrix corresponding to the cells. 
     However, the back electrode patterns  200  may not be limited to the above shape, but may have various shapes. 
     In addition, after the second insulating patterns  110  have been formed, the back electrode patterns  200  are formed among the second insulating patterns  110 , so the additional patterning process for the back electrode patterns  200  may not be necessary. 
     When the patterning process is performed by using a laser to form the back electrode patterns  200 , an edge region of the back electrode patterns may be delaminated or peeled off. However, according to the embodiment, the back electrode patterns can be formed without using the laser, so that the back electrode patterns  200  can be prevented from being deformed by the laser patterning. 
     Since the back electrode patterns  200  are not delaminated, the light absorption layer can be stably formed in the subsequent process, so that the quality and the efficiency of the solar cell can be improved. 
     In addition, although not shown in the drawings, the second insulating patterns  110  may be removed after the back electrode patterns  200  have been formed. 
     The method of forming the back electrode patterns  200  on the substrate  100  may not be limited to the above method. 
     For instance, as shown in  FIG. 18 , the substrate  100  is partially removed to form the second insulating patterns  110  extending from the substrate  100  and the back electrode patterns  200  are formed among the second insulating patterns  110 . 
     At this time, the second insulating patterns  110  and the substrate  100  are formed by using the same material. 
     After that, as shown in  FIG. 19 , the light absorption layer  300 , the first buffer layer  400  and the second buffer layer  500  are formed on the substrate  100  having the back electrode patterns  200  and the second insulating patterns  110 . 
     The light absorption layer  300  includes the Ib-IIIb-VIb group compound. 
     In detail, the light absorption layer  300  may include the Cu—In—Ga—Se (Cu(In,Ga)Se 2 ; CIGS) compound. 
     In contrast, the light absorption layer  300  may include the Cu—In—Se (CuInSe 2 ; CIS) compound or the Cu—Ga—Se (CuGaSe 2 ; CGS) compound. 
     For instance, in order to form the light absorption layer  300 , a CIG metal precursor layer is formed on the back electrode  201  by using a Cu target, an In target or a Ga target. 
     The metal precursor layer reacts with Se through the selenization process, thereby forming the CIGS light absorption layer  300 . 
     In addition, while the process for forming the metal precursor layer and the selenization process are being performed, alkali components contained in the substrate  100  are diffused into the metal precursor layer and the light absorption layer  300  through the back electrode patterns  200 . 
     The alkali components may improve the grain size of the light absorption layer  300  and the crystal property. 
     The light absorption layer  300  receives the incident light to convert the incident light into the electric energy. The light absorption layer  300  generates the photo-electromotive force based on the photoelectric effect. 
     At this time, since the second insulating patterns  110  are formed among the back electrode patterns  200 , the leakage current can be prevented from occurring among the back electrode patterns  200 . 
     The first buffer layer  400  can be formed by depositing CdS on the light absorption layer  300 . 
     The first buffer layer  400  is an N type semiconductor layer and the light absorption layer  300  is a P type semiconductor layer. Thus, the light absorption layer  300  and the first buffer layer  400  may form the PN junction. 
     In addition, the second buffer layer  500  can be formed by performing the sputtering process using the ZnO target. 
     The first and second buffer layers  400  and  500  are disposed between the light absorption layer  300  and the top electrode to be formed later. 
     Since there is great difference in the lattice constant and the energy bandgap between the light absorption layer  300  and the top electrode, if the first and second buffer layers  400  and  500  having the intermediate bandgap are interposed between the light absorption layer  300  and the top electrode, the superior junction can be obtained. 
     Then, as shown in  FIG. 20 , contact patterns  310  are formed through the light absorption layer  300 , the first buffer layer  400  and the second buffer layer  500 . 
     The contact patterns  310  can be formed through the mechanical patterning or the laser irradiation. 
     The back electrode patterns  200  are partially exposed through the contact patterns  310 . 
     After that, as shown in  FIG. 21 , a transparent conductive material is deposited on the second buffer layer  500  to form a top electrode and a connection wire  700 . 
     When the transparent conductive material is deposited on the second buffer layer  500 , the transparent conductive material is filled in the contact patterns  310  to form the connection wire  700 . 
     The back electrode patterns  200  are electrically connected to the top electrode  600  through the connection wire  700 . 
     In order to form the top electrode  600 , the sputtering process is performed with respect to the second buffer layer  500  by using aluminum-doped ZnO or alumina-doped ZnO. 
     The top electrode  600  is a window layer forming the PN junction with respect to the light absorption layer  300 . Since the top electrode  600  serves as a transparent electrode for the solar cell, the top electrode  600  is formed by using ZnO having high light transmittance and superior electric conductivity. 
     In addition, ZnO is doped with aluminum or alumina, so that the top electrode  600  has a low resistance value. 
     In order to form the top electrode  600 , a ZnO layer is deposited through the RF sputtering process using a ZnO target, the reactive sputtering using a Zn target, or the metal organic chemical vapor deposition (MOCVD). 
     In addition, a dual structure can be formed by depositing an ITO (indium tin oxide) layer having the superior electro-optical characteristic onto the ZnO layer. 
     Then as shown in  FIG. 22 , division patterns  320  are formed through the light absorption layer  300 , the first buffer layer  400  and the second buffer layer  500 . 
     That is, the division patterns  320  can be formed through the top electrode  600 , the light absorption layer  300 , the first buffer layer  400  and the second buffer layer  500 . 
     In addition, the division patterns  320  can be formed through the mechanical patterning or the laser irradiation. 
     The back electrode patterns  200  are partially exposed through the division patterns  320 . 
     The first buffer layer  400 , the second buffer layer  500  and the top electrode  600  are separated from each other by the division patterns  320 . In addition, the cells C 1  and C 2  are separated from each other by the division patterns  320 . 
     The first buffer layer  400 , the second buffer layer  500  and the light absorption layer  300  are aligned in the form of a stripe or a matrix by the division patterns  320 . 
     The division patterns  320  may not be limited to the above shape, but may have various shapes. 
     The cells C 1  and C 2  including the back electrode patterns  200 , the light absorption layer  300 , the first buffer layer  400 , the second buffer layer  500  and the top electrode  600  are formed by the division patterns  320 . The cell C 1  can be connected to the cell C 2  by the connection wire  700 . That is, the connection wire  700  electrically connects the back electrode patterns  200  of the second cell C 2  with the top electrode  600  of the first cell C 1  adjacent to the second cell C 2 . 
     After that, as shown in  FIG. 23 , a transparent resin  800  and a top substrate  900  are formed on the top electrode  600 . 
     The transparent resin  800  can be formed by performing the thermal process using EVA (ethylene vinyl acetate copolymer), and the top substrate  900  can be formed by using heat strengthened glass. 
     As described above, according to the solar cell and the method of fabricating the same of the third embodiment, second insulating patterns are formed among the back electrode patterns, so that coupling strength between the back electrode patterns and the second insulating patterns can be reinforced. 
     That is, since the coupling strength between the back electrode patterns and the second insulating patterns can be reinforced, the back electrode patterns can be prevented from being delaminated from the substrate. 
     When the patterning process is performed by using a laser to form the back electrode patterns, an edge region of the back electrode patterns may be delaminated or peeled off. However, according to the embodiment, the back electrode patterns can be formed without using the laser, so that the back electrode patterns can be prevented from being deformed by the laser patterning. 
     In addition, since the back electrode patterns may not be delaminated, the light absorption layer can be stably formed, so that the quality and efficiency of the solar cell can be improved. 
     Further, since the second insulating patterns are formed among the back electrode patterns, the leakage current can be prevented from occurring among the back electrode patterns.