Patent Publication Number: US-2012024378-A1

Title: Solar cell apparatus and method of fabricating the same

Description:
TECHNICAL FIELD 
     The embodiment relates to a solar cell apparatus and a method of fabricating the same. 
     BACKGROUND ART 
     Recently, as energy consumption has been increased, solar cells capable of converting solar energy into electric energy have 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 order to improve the performance of the solar cell, researches and studies have been carried out toward the enhancement of incident light efficiency. 
     DISCLOSURE 
     Technical Problem 
     The embodiment provides a solar cell apparatus capable of increasing light efficiency and a method of fabricating the same. 
     Technical Solution 
     According to the embodiment, a solar cell apparatus includes a solar cell, and an anti-reflective layer having a plurality of pores on the solar cell. 
     According to the embodiment, a solar cell apparatus includes a solar cell, and an anti-reflective layer on the solar cell. The anti-reflective layer includes a plurality of crystalline columns extending in a direction inclined with respect to a top surface of the solar cell. 
     According to the embodiment, a solar cell apparatus includes a solar cell, a first anti-reflective layer on the solar cell, and a second anti-reflective layer on the first anti-reflective layer. The first anti-reflective layer includes a plurality of first crystalline columns extending in a first direction inclined with respect to a top surface of the solar cell, and the second anti-reflective layer includes a plurality of second crystalline columns extending in a second direction inclined with respect to the top surface of the solar cell. 
     According to the embodiment, a method of fabricating a solar cell apparatus includes forming a solar cell on a support substrate, and forming an anti-reflective layer by spraying an anti-reflective material in a direction inclined with respect to a top surface of the solar cell. 
     Advantageous Effects 
     The solar cell apparatus according to the embodiment includes an anti-reflective layer including pores. Accordingly, the refractive index of the anti-reflective layer can be easily adjusted. The light efficiency of the solar cell apparatus can be improved by minimizing the reflection of a light incident from air (e.g., refractive index n=1) into a protective substrate or a top electrode layer. 
     In particular, since the anti-reflective layer has a porous structure due to pores, the anti-reflective layer has a refractive index lower than that of a dense structure. Therefore, the anti-reflective layer can reduce the rapid change of refractive indexes between the air and the protective substrate or between the air and the top electrode layer. 
     In other words, the quantity of sunlight reflected to the outside of the solar cell is reduced, and the quantity of sunlight absorbed into the solar cell is increased, so that the efficiency of the solar cell can be improved. 
     In addition, a plurality of anti-reflective layers include the same material, and are grown at angles different from each other. Accordingly, the refractive indexes of the anti-reflective layers including the same materials are gradually changed, so that superior anti-reflection effects can be represented. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIGS. 1 to 6  are sectional views showing a method of fabricating a solar cell apparatus according to a first embodiment; 
         FIG. 2  is a sectional view showing a solar cell apparatus according to a second embodiment; 
         FIG. 8  is an enlarged sectional view showing an anti-reflective film of a solar cell apparatus according to a third embodiment; 
         FIGS. 9 to 10  are sectional views showing a solar cell apparatus according to a fourth embodiment; 
         FIG. 11  is a sectional view showing a solar cell apparatus according to a fifth embodiment; 
         FIG. 12  is a graph showing the transmissivity in experimental example #3 and experimental example #1; 
         FIGS. 13 and 16  are sectional and plan views showing a TiO 2  layer in experimental examples #1, #2, and #3, and comparative example #1; and 
         FIGS. 17 and 18  are sectional views showing an MgF 2  layer in experimental example #8 and comparative example #2. 
     
    
    
     BEST MODE 
     Mode for Invention 
     In the description of the embodiments, it will be understood that, when a layer (or film), a region, a pattern, or a structure is referred to as being “on” or “under” another substrate, another layer (or film), another region, another pad, or another pattern, it can be “directly” or “indirectly” over the other substrate, layer (or film), region, pad, or pattern, 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 6  are sectional views showing a solar cell apparatus according to a first embodiment. 
     As shown in  FIG. 1 , a back electrode  200  is formed on a substrate  100 . 
     The substrate  100  includes a glass, or may include one a ceramic substrate such as alumina, a stainless still substrate, a titanium substrate, or a polymer substrate. In more detail, the substrate  100  may include sodalime glass. In addition, the substrate  100  may have a rigid property or a flexible property. 
     The back electrode  200  may include a metallic conductor. For example, the back electrode  200  may be formed through a sputtering process employing a molybdenum (Mo) target. 
     The Mo target is used because Mo represents high conductivity, ohmic contact with a light absorption layer, and high-temperature stability under a Se atmosphere. 
     The Mo thin film constituting the back electrode  200  must have low resistivity as an electrode and must have a superior adhesion property with respect to the substrate  100  such that the back electrode  200  is not delaminated from the substrate  10  due to a thermal expansion coefficient difference with the substrate  10 . 
     In addition, at least one back electrode  200  may be provided. When the back electrode  200  includes a plurality of layers  610 ,  620  . . . and  600   n,  the layers  610 ,  620  . . . and  600   n  constituting the back electrode  200  may include different materials. 
     Thereafter, as shown in  FIG. 2 , a light absorption layer  300  and a buffer layer  400  are formed on the back electrode  200 . The light absorption layer  300  includes a Ib-IIb-VIb-based compound. In more detail, the light absorption layer  300  includes copper-indium-gallium-selenide (Cu(In, Ga)Se 2 , CIGS)-based compound. 
     Differently, the light absorption layer  300  may include a copper-indium-selenide (CuInSe 2 , CIS)-based compound or a cooper-gallium-selenide (CuGaSe 2 , CIS)-based compound. 
     For example, in order to form the light absorption layer  300 , a CIG-based metallic precursor layer is formed on the back electrode  200  by using a Co target, an In target, and a Ga target. 
     Thereafter, the metallic precursor layer reacts with Se through a selenization process to form the CIGS-based light absorption layer  300 . 
     The light absorption layer  300  converts external incident light into electric energy. The light absorption layer  300  generates a photo-electromotive force based on a photo-electro effect. 
     At least one buffer layer  400  may be provided. For example, at least one buffer layer  400  may be formed by stacking a cadmium sulfide (CdS) layer. 
     In this case, the buffer layer  400  includes an N type semiconductor layer, and the light absorption layer  300  includes a P type semiconductor layer. Accordingly, the light absorption layer  300  and the buffer layer  400  construct a PN junction structure. 
     The buffer layer  400  may additionally include a zinc oxide (ZnO) layer formed on the CdS layer through a sputtering process using a ZnO target. The buffer layer  400  is interposed between the light absorption layer  300  and a top electrode layer  500  to be formed thereafter. 
     In other words, since the light absorption layer  300  and the top electrode layer  500  make a great difference in a lattice constant and an energy band gap, the buffer layer  400  having the intermediate energy band gap is interposed between the light absorption layer  300  and the top electrode layer  500 , so that junction is smoothly made. 
     As shown in  FIG. 3 , the top electrode layer  500  and the anti-reflective film  600  are formed on the buffer layer  400 . 
     The top electrode layer  500  may include a material selected from the group consisting of indium oxide (In 2 O 3 ), zinc oxide (ZnO) and tin oxide (SnO 2 ). The top electrode layer  500  is a window layer forming PN junction together with the light absorption layer  300 . Since the top electrode layer  500  serves as a transparent electrode on the entire surface of a solar cell  1 , the top electrode layer  500  includes a material representing high light transmissivity and electric conductivity. 
     In this case, an electrode having low resistance may be formed by doping aluminum (Al) or alumina into a ZnO layer. In addition, an ITO (Indium thin oxide) layer may be additionally formed on the front-side layer  500 . 
     Therefore, the solar cell  1  is formed on the substrate  100 . In other words, the solar cell  1  includes the back electrode  200 , the light absorption layer  300 , the buffer layer  400 , and the top electrode layer  500 . 
     The anti-reflective film  600  may be formed on the solar cell  1  through an evaporation process or a sputtering process. In more detail, the anti-reflective film  600  may be formed on a top surface of the solar cell  1 . In more detail, the anti-reflective film  600  may be coated on the top surface of the solar cell  1 . 
     In this case, the anti-reflective film  600  may be formed under a vacuum state. In addition, a source material  20  for the anti-reflective film  600  is sprayed by a target or a source, and deposited on the top electrode layer  500 , so that the anti-reflective film  600  is formed. 
     As shown in  FIG. 4 , the spray direction of the source material  20  is inclined with respect to the substrate  100 . For example, the source material  20  may be sprayed in a direction inclined with respect to the substrate  100 . In addition, the source material  20  may be sprayed onto the substrate  100  in a state that the substrate  100  is inclined. 
     For example, the source material  20  may be sprayed onto the substrate  100  in the stat that the substrate  100  is inclined at an angle of about 40° to about 80° with respect to a plane perpendicular to the spray direction of the source material  20 . In other words, the source  10  may spray the source material  20  onto the substrate  100  in the state that the source  10  is inclined at an angle of about 40° to about 80° with respect to a direction perpendicular to the top surface of the top electrode layer  500 . 
     In other words, the source  10  sprays the source material  20  used to form a first anti-reflective layer  610  in a direction inclined with respect to the top surface of the solar cell  1 , that is, the top surface of the top electrode layer  500 . In other words, on the assumption that the vertical direction refers to an angle of 0°, the source  10  sprays the source material  20  onto the substrate  100  at an angle a of about 40° to about 80°. 
     Therefore, as shown in  FIGS. 3 ,  5 , and  6 , a plurality of crystalline columns  601  are grown in the direction inclined with respect to the top surface of the top electrode layer  500 . In other words, the crystalline columns  601  extend in the direction inclined with respect to the top surface of the solar cell  1 , that is, the top surface of the top electrode layer  500 . In more detail, the crystalline columns  601  extend upward from the top surface of the top electrode layer  500 . In other words, the crystalline columns  601  extend in the direction inclined with respect to the top electrode layer  500 . 
     The crystalline columns  601  may form an angle β 1  of about 10° to about 50° with respect to the top surface of the top electrode layer  500 . As described above, as the crystalline columns  601  are formed, the anti-reflective film  600  is formed on the top electrode layer  500 . 
     A plurality of pores  602  are formed between the crystalline columns  601 . In other words, since the crystalline columns  601  are not densely formed on the top surface of the top electrode layer  500 , the pores  602  are formed. The diameters or the widths of the pores  602  may be 1/20 to about ⅕ of the diameters or the widths of the crystalline columns  601 . 
     The pores  602  may extend in the extension direction of the crystalline columns  601 . Upper portions of the pores  602  may be open on the top surface of the anti-reflective film  600 . 
     Therefore, the anti-reflective film  600  has a porous structure. In other words, the anti-reflective film  600  may not have a dense structure. In more detail, the anti-reflective film  600  may have a more porous structure and a less dense structure as the crystalline columns  601  are inclined. 
     Referring to  FIGS. 5 and 6 , the method of forming the anti-reflective film  600  will be described in detail. In order to form the anti-reflective film  600 , when a deposition process is performed, a core  30  is formed on the top electrode layer  500 , and the source material  20  is deposited near the core  30 , so that the crystalline columns  601  are grown. 
     In this case, the source material  20  is injected into the top electrode layer  500  at a predetermined angle, and the pores  602  are formed due to a shadow effect to generate a shadow area  40 , so that the anti-reflective film  600  has a porous structure. 
     Since the anti-reflective film  600  has a porous structure, a refractive index is more reduced on the anti-reflective film  600  as compared with that of a thin film having a dens structure. Accordingly, the solar cell  1  can represent lower reflectance and improved transmissivity due to the anti-reflective film  600 . In other words, the anti-reflective film  600  can increase anti-reflection efficiency. 
     For example, the anti-reflective film  600  may have a refractive index of about 1.18 to about 1.32. In more detail, the anti-reflective film  600  may have the refractive index of about 1.18 to about 1.29. In more detail, the anti-reflective film  600  may have a refractive index of about 1.18 to about 1.26. 
     The anti-reflective film  600  is transparent. The anti-reflective film  600  may include fluoride such as magnesium fluoride (e.g., MgF 2 ) and oxide such as indium tin oxide (ITO), silicon oxide (SiO 2 ), zinc oxide (ZnO) or titanium oxide (e.g., TiO 2 ). 
     The refractive index of the anti-reflective film  600  varies according to the spray angle of the source material  20 . In other words, according to the method of fabricating a solar cell apparatus of the first embodiment, the anti-reflective film  600  may have a desired refractive index. In other words, the source material  20  is deposited on the top surface of the top electrode layer  500  at a desired angle, so that the anti-reflective film  600  may have the optimal refractive index to increase the quantity of light incident into the solar cell  1  as much as. 
     Therefore, the anti-reflective film  600  can reduce the rapid change between the air layer and the top electrode layer  500 . Accordingly, the quantity of sunlight reflected by the top surface of the top electrode layer  500  can be reduced. 
       FIG. 7  is a sectional view showing a solar cell apparatus according to a second embodiment. In the following description about the present embodiment, the structures and components identical to those of the previous embodiments will not be further described except for the additional description about the anti-reflective film. The solar cell apparatus according to the second embodiment may be substantially identical to the solar cell apparatus according to the previous embodiment, except for several parts. 
     Referring to  FIG. 7 , the anti-reflective film  600  may include a plurality of layers  610 ,  620 , . . . , and  600   n.  In this case, crystalline columns may extend in different directions at the different layers  610 ,  620 , . . . , and  600   n.  For example, the angles β 2  and β 3  between the crystalline columns  601  and the top surface of the solar cell  1  vary according to the layers  610 ,  620 , . . . , and  600   n.  Accordingly, the layers  610 ,  620 , . . . , and  600   n  may have refractive indexes different from each other. 
     In this case, the processes of forming the layers  610 ,  620 , and  600   n  may be performed by spraying a source material on the top electrode layer  500  at angles different from each other. For example, the source material may be sprayed at a first angle to form the first layer. The source material may be sprayed at a second angle to form the second layer. The source material may be sprayed at a third angle to form the third layer. 
     For example, the anti-reflective film  600  may include the first and second anti-reflective layers  610  and  620 . 
     The first anti-reflective layer  610  is formed on the solar cell  1 . In more detail, the first anti-reflective layer  610  is formed on the top surface of the solar cell  1 . In more detail, the first anti-reflective layer  610  is coated on the top surface of the solar cell  1 . 
     The first anti-reflective layer  610  includes first crystalline columns  611 . The first crystalline columns  611  extend in a first direction. In this case, the angle β 2  between the first crystalline columns  611  and the top surface of the top electrode layer  500  may be in the range of about 10° to about 50°. 
     The second anti-reflective layer  620  is formed on the first anti-reflective layer  610 . In more detail, the second anti-reflective layer  620  is formed on the top surface of the first anti-reflective layer  610 . The second anti-reflective layer  620  is coated on the top surface of the first anti-reflective layer  610 . 
     The second anti-reflective layer  620  includes a plurality of second crystalline columns  621 . The second crystalline columns  621  extend in a second direction different from the first direction. In this case, the angle β 3  between the second crystalline columns  621  and the top electrode layer  500  may be in the range of about 10° to about 50°. 
     In this case, the angle β 2  between the first crystalline columns  611  and the top surface of the top electrode layer  500  may be different from the angle β 3  between the second crystalline columns  621  and the top surface of the top electrode layer  500 . For example, the angle β 2  between the first crystalline columns  611  and the top surface of the top electrode layer  500  may be greater than the angle β 3  between the second crystalline columns  621  and the top surface of the top electrode layer  500 . 
     In addition, a third anti-reflective layer including a plurality of third crystalline columns extending in the third direction may be formed on the second anti-reflective layer  620 . In addition, a fourth anti-reflective layer may be formed on the third anti-reflective layer. 
     Therefore, the above anti-reflective layers  610 ,  620 , . . . , and  600   n  may have refractive indexes different from each other. In addition, according to the present embodiment, the solar cell apparatus includes the anti-reflective film  600  including the anti-reflective layers  610 ,  620 , . . . , and  600   n  having the refractive indexes different from each other. 
     For example, the first anti-reflective layer  610  may have a higher refractive index, and the second anti-reflective layer  620  may have a lower refractive index. In addition, the third anti-refractive layer may have a refractive index lower than that of the second anti-reflective layer  620 . 
     In addition, a higher layer among the anti-reflective layers  610 ,  620 , . . . , and  600   n  may have a lower refractive index. In contrast, the higher layer among the anti-reflective layers  610 ,  620 , . . . , and  600   n  may have a higher refractive index. In addition, each anti-reflective layer having a higher refractive index may be alternately aligned with an anti-reflective layer having a lower refractive index. 
     In particular, if the layers  610 ,  620  . . . and  600   n  have the refractive index gradually lowered from the top surface of the solar cell  1  to the air layer, that is, if the refractive index of the layers  610 ,  620  . . . and  600   n  is gradually reduced in the upward direction, the refractive index of the anti-reflective film is gradually reduced in the upward direction. Accordingly, the anti-reflective film  600  can effectively reduce the difference in the refractive indexes between the air and the top electrode layer  500 . 
     The anti-reflective layers  610 ,  620 , . . . , and  600   n  of the anti-reflective film  600  may include the same material. In other words, the first anti-reflective layer  610 , the second anti-reflective layer  620 , and the third anti-reflective layer may include the same material. 
     As described above, the refractive indexes of the anti-reflective layers  610 ,  620 , and . . .  600   n  are set to desired values, respectively, so that the optimal anti-reflection effect can be realized. Therefore, the solar cell apparatus according to the present embodiment can represent improved generating efficiency. 
       FIG. 8  is an enlarged sectional view showing an anti-reflective film of a solar cell apparatus according to a third embodiment. 
     In the following description about the present embodiment, the structures and components identical to those of the previous embodiments will not be further described except for the additional description for the anti-reflective film and modifications. The solar cell apparatus according to the third embodiment may be substantially identical to the solar cell apparatus according to the previous embodiment, except for several parts. 
     Referring to  FIG. 8 , crystalline columns  611 ,  621 , and  631  of the anti-reflective layers may be formed in a zig-zag pattern. For example, the crystalline columns  611  of the first anti-reflective layer extend in one upward direction with respect to the plane VS perpendicular to the top surface of the solar cell  1 , and the crystalline columns  621  of the second anti-reflective layer may extend in another upward direction of the perpendicular plane VS. In addition, the crystalline columns  631  may extend in the one upward direction. 
     For example, the first crystalline columns  611  may extend in a right upward direction RD on the basis of the perpendicular plane VS, and the second crystalline columns  621  may extend in a left upward direction LD with respect to the perpendicular plane VS. Similarly, the third crystalline columns  631  of the third anti-reflective layer may extend in the right upward direction RD of the perpendicular plane VS. 
     In this case, the crystalline columns  611 ,  621 , and  631  of the anti-reflective layers may be inclined at the same angle or different angles with respect to the top surface of the solar cell  1 . For example, the angle between the first crystalline columns  611  and the top surface of the solar cell  1  may be identical to or different from the angle between the second crystalline columns  621  and the top surface of the solar cell  1 . 
       FIGS. 9 and 10  are sectional views showing an anti-reflective film of a solar cell apparatus according to a fourth embodiment. In the following description about the present embodiment, the structures and components identical to those of the previous embodiments will not be further described except for the additional description for an external anti-reflective film. The solar cell apparatus according to the fourth embodiment may be substantially identical to the solar cell apparatus according to the previous embodiment, except for several parts. 
     Referring to  FIG. 9 , a transparent resin  700  and a protective substrate  800  are formed on the anti-reflective film  600 . 
     The transparent resin  700  may be formed through a thermal process using EVA (ethylene vinyl acetate copolymer), and the protective substrate  800  may include half-strengthened glass. 
     Thereafter, as shown in  FIG. 10 , an external anti-reflective film  900  is formed on the protective substrate  800 . In more detail, the external anti-reflective film  900  is formed on the top surface of the protective substrate  900 . In more detail, the external anti-reflective film  900  may be coated on the top surface of the protective substrate  900 . 
     Similarly to the method of forming the anti-reflective film  600  according to the previous embodiments, the external anti-reflective film  900  may be formed through an evaporation process or a sputtering process. 
     Similarly, the external anti-reflective film  900  may have the same structure as that of the anti-reflective film  600  according to the previous embodiments. In other words, the external anti-reflective film  900  includes a plurality of crystalline columns  901  extending in a direction inclined with respect to the top surface of the protective substrate  800 . The crystalline columns  901  extend upward from the top surface of the protective substrate  800 . 
     For example, an angle β 4  between the crystalline columns  901  and the top surface of the protective substrate  800  may be in the range of about 10° to about 50°. 
     Due to the external anti-reflective film  900 , the quantity of sunlight reflected from the top surface of the protective substrate  800  can be reduced, and the transmissivity can be improved. In other words, the anti-reflection efficiency can be increased by the external anti-reflective film  900 . 
     In addition, the external anti-reflective film  900  may be formed on a bottom surface of the protective substrate  800  as well as the top surface of the protective substrate  800 . 
       FIG. 11  is a sectional view showing a solar cell apparatus according to a fifth embodiment. In the following description about the present embodiment, the structures and components identical to those of the previous embodiments will not be further described except for the additional description for an external anti-reflective film. The solar cell apparatus according to the fifth embodiment may be substantially identical to the solar cell apparatus according to the previous embodiment, except for several parts. 
     Referring to  FIG. 11 , the external anti-reflective film  900  may include a plurality of layers  910 ,  920 , . . . and  900   n.  In addition, the external anti-reflective film  900  may be formed similarly to a process of forming an anti-reflective film having a multiple layer structure according to the previous embodiments and have a structure similar to that of the anti-reflective film having a multiple layer structure. 
     Due to the external anti-reflective film  900 , the quantity of sunlight reflected from the top surface of the protective substrate  800  can be reduced, and the transmissivity can be improved. In other words, the anti-reflection efficiency can be increased by the external anti-reflective film  900 . 
     In particular, the layers  910 ,  920 , . . . , and  900   n  of the external anti-reflective film  900  may have desired refractive indexes. Therefore, the external anti-reflective film  900  can effectively reduce the difference in the refractive index between the air layer and the protective substrate  800 . 
     Therefore, the solar cell apparatus according to the present embodiment can represent improved generating efficiency. 
     Although the exemplary embodiments of the present invention have been described, it is understood that the present invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed. 
     EXPERIMENTAL EXAMPLES #1, #2, AND #3, AND COMPARATIVE EXAMPLE #1 
     A sputtering process is performed to deposit TiO 2  on a glass substrate in an inclination direction and a vertical direction. In ex examples #1, #2, and #3, and comparative example #1, the glass substrate is inclined at an angle of about 45°, about 60°, about 80°, or 0° with respect to a plane perpendicular to the spray direction of TiO 2 . The transmissivity in experimental example #3 and comparative example #1 is shown in  FIG. 12 . In addition, the sectional and plan views of the TiO 2  layer in experimental examples #1, #2, and #3 and comparative example #1 are shown in  FIGS. 13 to 16 . 
     EXPERIMENTAL EXAMPLES #4, #5, #6, #7, AND #8, AND COMPARATIVE EXAMPLE #2 
     A sputtering process is performed to deposit MgF 2  on a glass substrate at a predetermined thickness in an inclination direction and a vertical direction. In Experimental Examples #4, #5, #6, #7, and #8, and Comparative example #2, inclination angles α of the glass substrate with respect to a plane perpendicular to the spray direction of MgF 2  and the refractive indexes of MgF 2  layer according to the inclination angles α are shown in table 1. The sectional shapes of the MgF 2  layer according to Experimental Example #8 and Comparative Example #2 are shown in  FIGS. 17 and 18 . As shown in Table 1, the refractive index of the MgF 2  layer may be set to various values according to the inclination angles. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Inclination Angle 
                 Refractive index 
               
               
                   
                 of Glass Substrate 
                 of MgF 2  layer 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Experimental 
                 20 
                 1.373 
               
               
                   
                 Example #4 
               
               
                   
                 Experimental 
                 40 
                 1.363 
               
               
                   
                 Example #5 
               
               
                   
                 Experimental 
                 60 
                 1.327 
               
               
                   
                 Example #6 
               
               
                   
                 Experimental 
                 70 
                 1.266 
               
               
                   
                 Example #7 
               
               
                   
                 Experimental 
                 80 
                 1.191 
               
               
                   
                 Example #8 
               
               
                   
                 Comparative 
                 0 
                 1.376 
               
               
                   
                 Example #2 
               
               
                   
                   
               
            
           
         
       
     
     INDUSTRIAL APPLICABILITY 
     The embodiment is applicable to a solar cell apparatus.