Patent Publication Number: US-2011073153-A1

Title: Photovoltaic device and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The entire disclosure of Japanese Patent Applications No. 2009-222254 filed on Sep. 28, 2009 and 2010-191817 filed on Aug. 30, 2010, including specification, claims, drawings, and abstract, is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a photovoltaic unit and a manufacturing method of a photovoltaic unit. 
     2. Background Art 
     Solar cells are known which use polycrystalline, microcrystalline, or amorphous silicon. In particular, a solar cell having a structure in which thin films of microcrystalline or amorphous silicon are layered has attracted much attention in view of reduced resource consumption, cost reduction, and improved efficiency. 
       FIG. 2  is a cross sectional schematic view showing a basic structure of a photovoltaic device  100 . The photovoltaic device  100  generally has a structure in which a transparent electrode  12 , a photovoltaic unit  14 , and a backside electrode  16  are layered over a transparent substrate  10  such as glass, and generates electric power by allowing light to enter through the transparent substrate  10 . A manufacturing method and a patterning device for integrating such photovoltaic devices in series are known (for example, in Patent Literature 1). 
       FIGS. 3A-3F  show a manufacturing process of the photovoltaic device  100  in the related art. In  FIGS. 3A-3F , a plan view and cross sectional views are schematically shown for each step of the manufacturing process of the photovoltaic device  100 . The cross sectional views show cross sections along a line A-A in the plan view and cross sections along a line B-B in the plan view. 
     In step S 10 , as shown in  FIG. 3A , a slit S 1  which divides the transparent electrode  12  formed over the transparent substrate  10  is formed through laser patterning and a slit S 2  is formed through laser patterning in a direction perpendicular to the slit S 1 . In step S 12 , as shown in  FIG. 3B , the photovoltaic unit  14  is formed covering the transparent electrode  12 . As the photovoltaic unit  14 , an amorphous silicon (a-Si) photovoltaic unit, a microcrystalline (μc-Si) photovoltaic unit, or a tandem structure of these photovoltaic units may be employed. In step S 14 , as shown in  FIG. 3C , a slit S 3  which divides the photovoltaic unit  14  is formed through laser patterning at a position near the slit S 1  and not overlapping the slit S 1 , and along a direction of the slit S 1 . In step S 16 , as shown in  FIG. 3D , the backside electrode  16  is formed covering the photovoltaic unit  14 . In step S 18 , as shown in  FIG. 3E , a slit S 4  which divides the photovoltaic unit  14  and the backside electrode  16  is formed through laser patterning at a position near the slit S 3  and not overlapping the slits S 1  and S 3 , and along the direction of the slits S 1  and S 3 . With this process, a structure in which a plurality of photovoltaic cells are connected in series along the direction of the slit S 2  is obtained. In step S 20 , as shown in  FIG. 3F , a slit S 5  which divides the photovoltaic unit  14  and the backside electrode  16  formed in the slit S 2  is formed through laser patterning. 
     In this manner, photovoltaic cells adjacent in the direction of the slit S 1  are electrically separated from each other, and a structure is obtained in which a plurality of photovoltaic cell groups, each including a plurality of photovoltaic cells connected in series, are aligned. The photovoltaic cell groups are finally connected in parallel to each other, and the photovoltaic device  100  is formed. 
     In addition, in step S 20 , the slit S 5  is also formed as an insulating groove  18  in a panel periphery of the photovoltaic device  100 , to electrically insulate the outside and a panel end of the photovoltaic device  100  from each other. 
     A technique is also known in which an end of the backside electrode  16  of the photovoltaic device  100  is placed at a more inward position of the panel than an end of the photovoltaic unit  14 , to improve the insulating characteristic at the panel periphery of the photovoltaic device  100 . 
     In the thin film solar cells of the related art, when the thin film solar cell is used outdoors, there may be cases where moisture enters from a sealing portion of the end of the photovoltaic device  100 , causing, in the structure where the insulating groove  18  and the backside electrode  16  are placed at inner positions, reduction of electrical insulation at the panel periphery, detachment of the photovoltaic unit  14 , or formation of a short-circuiting path due to contact between the transparent electrode  12  and the backside electrode  16 . 
     In order to secure sufficient electrical insulation at the panel periphery, the laser power when the slit S 5  is formed must be set at a high power. However, such a configuration may cause damage in the end surface of the photovoltaic unit  14 , possibly resulting in a short-circuiting path. In addition, in the case of a small-size solar cell which is used for indoor light and in which the possibility of moisture intrusion is low, such a solar cell is formed with a large-area substrate and then cutting the substrate into a predetermined size. During this process, the transparent electrode  12  and the backside electrode  16  at the end of each photovoltaic device  100  may contact each other at the cut surface, resulting in a short-circuiting path. Therefore, the slits S 2  and S 5  must be formed, resulting in a reduction of effective area for power generation. 
     SUMMARY 
     According to one aspect of the present invention, there is provided a photovoltaic device wherein a plurality of photovoltaic cells in which a first electrode, a power generation layer, and a second electrode are sequentially layered over a substrate are connected in series, and the photovoltaic device comprises ends of the power generation layer and the second electrode at a periphery of the photovoltaic device and extending in a direction of the series connection, and an insulating groove formed in a region near a insulating groove the ends and parallel to the ends and formed by leaving the first electrode and removing at least the second electrode. 
     According to another aspect of the present invention, there is provided a method of manufacturing a photovoltaic device, comprising forming a plurality of photovoltaic cells, in which a first electrode, a power generation layer, and a second electrode are sequentially layered over a substrate, in series connection to each other, forming a separating groove at a periphery of the photovoltaic device in a direction intersecting the direction of the series connection by removing the first electrode, the power generation layer, and the second electrode, and forming an insulating groove in a region near the separating groove and parallel to the separating groove by leaving the first electrode and removing at least the second electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the present invention will be described in detail based on the following drawings, wherein: 
         FIG. 1A  is a plan view and cross sectional views showing a manufacturing process of a photovoltaic device according to a preferred embodiment of the present invention; 
         FIG. 1B  is a plan view and cross sectional views showing the manufacturing process of the photovoltaic device according to the preferred embodiment of the present invention; 
         FIG. 1C  is a plan view and cross sectional views showing the manufacturing process of the photovoltaic device according to the preferred embodiment of the present invention; 
         FIG. 1D  is a plan view and cross sectional views showing the manufacturing process of the photovoltaic device according to the preferred embodiment of the present invention; 
         FIG. 1E  is a plan view and cross sectional views showing the manufacturing process of the photovoltaic device according to the preferred embodiment of the present invention; 
         FIG. 2  is a cross sectional view showing a basic structure of a photovoltaic device; 
         FIG. 3A  is a plan view and cross sectional views showing a manufacturing process of a photovoltaic device of related art; 
         FIG. 3B  is a plan view and cross sectional views showing the manufacturing process of the photovoltaic device of related art; 
         FIG. 3C  is a plan view and cross sectional views showing the manufacturing process of the photovoltaic device of related art; 
         FIG. 3D  is a plan view and cross sectional views showing the manufacturing process of the photovoltaic device of related art; 
         FIG. 3E  is a plan view and cross sectional views showing the manufacturing process of the photovoltaic device of related art; 
         FIG. 3F  is a plan view and cross sectional views showing the manufacturing process of the photovoltaic device of related art; 
         FIG. 4  is a diagram showing an example structure of a photovoltaic device according to a preferred embodiment of the present invention; 
         FIG. 5  is a diagram showing a power generation characteristic of a photovoltaic device; 
         FIG. 6  is a diagram showing an equivalent circuit of the photovoltaic device shown in  FIG. 4 ; 
         FIG. 7  is a diagram showing a relationship of a power generation output with respect to a distance between slits S 5  and S 6  of a photovoltaic device; 
         FIG. 8  is a diagram showing a relationship of a power generation output with respect to a distance between the slits S 5  and S 6  of a photovoltaic device; and 
         FIG. 9  is a diagram showing a relationship of a power generation output with respect to a distance between the slits S 5  and S 6  of a photovoltaic device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIGS. 1A-1E  show a manufacturing process of a photovoltaic device  200  according to a preferred embodiment of the present invention.  FIGS. 1A-1E  schematically show plan views and cross sectional views in the steps of the manufacturing process of the photovoltaic device  200 . The cross sectional views show cross sections along a line C-C in the plan views and cross sections along a line D-D in the plan views. 
     In step S 30 , as shown in  FIG. 1A , a slit S 1  (in the left and right direction in the figure) which divides a transparent electrode  12  formed over a transparent substrate  10  is formed through laser patterning, and a slit S 2  (in the up and down direction in the figure) is formed in a direction perpendicular to the slit S 1 . In this process, the slit S 2  which becomes a insulating groove  18  is also formed in a panel periphery of the photovoltaic device  200 . 
     For the transparent substrate  10 , a material which transmits light of a wavelength used in photovoltaic in the solar cell is used, such as, for example, glass, plastic, etc. For the transparent electrode  12 , a transparent conductive oxide in which tin (Sn), antimony (Sb), fluorine (F), aluminum (Al), or the like is doped into tin oxide (SnO 2 ), zinc oxide (ZnO), indium tin oxide (ITO), or the like may be used. 
     A laser device for forming the slits S 1  and S 2  preferably uses a YAG laser of a wavelength of 1064 nm. A laser beam emitted from the laser device is irradiated from the side of the transparent electrode  12  while the power of the laser beam is adjusted, and is continuously scanned in the direction of the slit S 1  and the direction of the slit S 2  which is perpendicular to the direction of the slit S 1 , so that the slits S 1  and S 2  can be formed. The laser for forming the slits S 1  and S 2  may alternatively be irradiated from the side of the transparent substrate  10 . 
     Because a large number of slits S 1  must be formed in order to integrate a large number of photovoltaic cells in series, it is preferable to use a multi-emission laser device in which a plurality of laser beam emission outlets are placed at equal distances along the direction perpendicular to the slit S 1 . For example, a laser device in which 2-5 laser beam emission outlets are placed is preferably used. With this process, a large number of slits S 1  for integrating a large number of photovoltaic cells in series can be quickly formed. Because a size of the slit S 2  may be larger than the sizes of the other slits and the patterning precision of the slit S 2  may be lower than the other slits, the setting of the patterning conditions is simple even if the multi-emission laser device is used. 
     In step S 32 , as shown in  FIG. 1B , a photovoltaic unit  14  is formed covering the transparent electrode  12  and the slits S 1  and S 2 . The photovoltaic unit  14  is not particularly limited, and may be, for example, an amorphous silicon (a-Si) photovoltaic unit, a microcrystalline (μc-Si) photovoltaic unit, or a tandem structure of these photovoltaic units. The photovoltaic unit  14  can be formed using plasma CVD or the like. 
     In step S 34 , as shown in  FIG. 1C , a slit S 3  which divides the photovoltaic unit  14  is formed through laser patterning. The slit S 3  is formed at a position near the slit S 1  and not overlapping the slit S 1 , along the direction of the slit S 1 , and towards a surface of the transparent electrode  12 . 
     For a laser device for forming the slit S 3 , a YAG laser (second harmonic) of a wavelength of 532 nm is preferably used. A laser beam emitted from the laser device is irradiated from the side of the transparent substrate  10  while the power of the laser beam is adjusted, and is scanned in the direction of the slit S 3 , so that the slit S 3  can be formed. 
     In step  36 , as shown in  FIG. 1D , a backside electrode  16  is formed covering the photovoltaic unit  14  and the slit S 3 . The backside electrode  16  is preferably made of a reflective metal. Alternatively, the backside electrode  16  may have a layered structure of the reflective metal and a transparent conductive oxide (TCO). For the metal electrode, silver (Ag), aluminum (Al), or the like may be used. For the transparent conductive oxide (TCO), tin oxide (SnO 2 ), zinc oxide (ZnO), indium tin oxide (ITO), or the like may be used. 
     In step S 38 , as shown in  FIG. 1E , slits S 4 , S 5 , and S 6  which divide the photovoltaic unit  14  and the backside electrode  16  are formed through laser patterning. The slit S 4  is formed at a position near the slit S 3  and not overlapping slits S 1  and S 3 , along the direction of the slits S 1  and S 3 , and to a surface of the transparent electrode  12  in a manner to divide the photovoltaic unit  14  and the backside electrode  16 . With this configuration, a structure is obtained in which a plurality of photovoltaic cells are connected in series along the direction of the slit S 2 . 
     The slit S 5  is formed in a region where the slit S 2  is formed, to the surface of the transparent electrode  12  in a manner to divide the photovoltaic unit  14  and the backside electrode  16  formed in the slit S 2 . Because the slit S 5  is formed in a direction of the series connection, the photovoltaic cells adjacent in the direction of the slit S 1  are electrically separated from each other. In addition, the slit S 5  is also formed in the slit S 2  formed at the panel periphery of the photovoltaic device  200  and which becomes the separating groove  18 , to electrically separate the photovoltaic unit  14  and the backside electrode  16  at the panel periphery and the photovoltaic unit  14  and the backside electrode  16  at the inner side of the panel from each other. 
     Because the slit S 5  is formed in the region where the slit S 2  is formed, the irradiation of laser light from the side of the transparent electrode  12  is enabled, and when the slit S 4  is formed, the slit S 5  is formed continuously. 
     Further, the slit S 6  is formed. The slit S 6  becomes a separating groove  20 . The slit S 6  is formed by removing at least the backside electrode  16  and leaving only the transparent electrode  12  in a region further inward in the panel than the separating groove  18 . For example, the slit S 6  is formed by removing the photovoltaic unit  14  and the backside electrode  16  and leaving only the transparent electrode  12 . In addition, the slit S 6  is preferably formed parallel to the slits S 2  and S 5  which become the separating groove  18 . 
     Next, a preferable position of the slit S 6  of the photovoltaic device  200  is determined.  FIG. 4  shows a structure of a photovoltaic panel formed for determining a preferable position of the slit S 6  of the photovoltaic device  200 . In the example configuration of  FIG. 4 , a length of the photovoltaic cell having a tandem structure of an amorphous silicon (a-Si) photovoltaic unit and a microcrystalline silicon (μc-Si) photovoltaic unit as the photovoltaic unit  14  is 90 mm, and 9 stages of arrays of the photovoltaic cells are formed. 
       FIG. 5  shows an actual measurement value of a power generation characteristic of the photovoltaic device  200  with respect to a distance between the slits S 5  and S 6 . A wide solid line represents an initial power generation characteristic of 1 stage of the photovoltaic cells when the slit S 6  is formed at a position distanced from the slit S 5  by 5 mm. A dot-and-chain line represents an initial power generation characteristic of 1 stage of the photovoltaic cells when the slit S 6  is formed at a position distanced from the slit S 5  by 5 mm and the slit S 5  is completely electrically short-circuited. A dotted line represents an initial power generation characteristic of 1 stage of the photovoltaic cells when the slit S 6  is not formed (that is, a structure corresponding to a structure in which the slit S 6  is formed at a position distanced from the slit S 5  by 90 mm), and the slit S 5  is completely electrically short-circuited. 
     As shown in  FIG. 6 , an equivalent circuit of the photovoltaic device  200  of  FIG. 4  is represented as a structure in which 1 stage of the photovoltaic cells is divided into a first cell region and a second cell region with an area ratio of 85:5 by the slit S 6 , and the first and second cell regions are connected by a series resistance rs and a parallel resistance rsh. In consideration of this, fitting is executed on the power generation characteristic of  FIG. 5  with the series resistance rs of the equivalent circuit of  FIG. 6  fixed and the parallel resistance rsh of the equivalent circuit of  FIG. 6  being set as a parameter, and the parallel resistance rsh is determined for a case where the slit S 6  is formed at a position distanced from the slit S 5  by 5 mm and a case where the slit S 6  is not formed. The parallel resistance rsh with respect to the distance from the slit S 5  is then determined assuming that the parallel resistance rsh changes exponentially with respect to the distance from the slit S 5 , as shown by the following equation (1). 
         rsh=Aexp (− Bx )  [Equation 1]
 
     wherein A and B are coefficients. 
     The parallel resistance rsh determined through the above-described method is applied to the equivalent circuit shown in  FIG. 6 , and a change of the power generation output with respect to the distance of the slit S 6  from the slit S 5  is calculated for cases where the length of the photovoltaic cell is 90 mm, 300 mm, and 600 mm.  FIG. 7  shows the change of the power generation output when the length of the photovoltaic cell is 90 mm,  FIG. 8  shows the change of the power generation output when the length of the photovoltaic cell is 300 mm, and  FIG. 9  shows the change of the power generation output when the length of the photovoltaic cell is 600 mm. 
     As shown in  FIGS. 8 and 9 , the power generation output of the photovoltaic device  200  gradually decreases up to the distance of the slit S 6  from the slit S 5  of approximately 100 mm, the slope of reduction becomes steep after the distance exceeds 100 mm, and the slope again becomes gradual as the distance becomes larger. Therefore, the slit S 6  (second insulating grove  20 ) is preferably formed in a range in which the power generation output of the photovoltaic device  200  is not rapidly reduced, that is, in a region within 100 mm from the slit S 5  (separating groove  18 ). In particular, the slit S 6  is preferably formed in a region near the slit S 5  in which short-circuiting tends to occur, that is, in a region within 10 mm from the slit S 5 . 
     For a laser device for forming the slits S 4 , S 5 , and S 6 , a YAG laser (second harmonics) of a wavelength of 532 nm is preferably used. A laser beam emitted from the laser device is irradiated from the side of the transparent substrate  10  while the power of the laser beam is adjusted, and is scanned in the directions of the slits S 4 , S 5 , and S 6 , so that the slits S 4 , S 5 , and S 6  can be formed. 
     As described above, the slits S 1 , S 3 , and S 4  are formed to connect adjacent photovoltaic cells in series, and the slits S 2  and S 5  are formed to align the photovoltaic cell groups, in which the photovoltaic cells are connected in series, with each other. With such a configuration, a structure is obtained in which the photovoltaic cells adjacent in the direction of the slit S 1  are electrically separated, and a plurality of photovoltaic cell groups, in each of which a plurality of photovoltaic cells are connected in series, are provided aligned with each other. The photovoltaic cell groups are finally connected in parallel to each other, to form the photovoltaic device  200 . 
     In the separating groove  18 , all of the transparent electrode  12 , the photovoltaic unit  14 , and the backside electrode  16  formed over the transparent substrate  10  are removed. The separating groove  18  maintains the electrical insulation between the outside and the panel at the panel periphery of the photovoltaic device  200 . 
     The insulating groove  20  is formed at a more inward position in the panel than the separating groove  18 . The insulating groove  20  is formed as a groove in which at least the backside electrode  16  is removed. By forming the insulating groove  20  in addition to the separating groove  18 , it is possible to maintain a high electrical insulation between the peripheral portion and the more inward portion than the insulating groove  20 , even when the electrical insulation between the outside and the panel due to the separating groove  18  is degraded. 
     In addition, because the backside electrode in a portion near the separating groove  18  and the backside electrode in the other portions can be insulated by the insulating groove  20 , the cell regions on both sides of the insulating groove are electrically connected primarily by the transparent electrode. Because the transparent electrode is a transparent conductive film, the resistivity is higher compared to a metal. Therefore, in the integrated solar cell, influences of defects such as short-circuiting of a portion near the separating groove  18  can be reduced, and at the same time, electrical energy generated in the portion near the first insulting groove  18  can be extracted, resulting in an increased output. 
     In addition, the insulating groove  20  is formed as a groove in which at least the backside electrode  16  is removed. The slit S 6  which becomes the insulating groove  20  can be formed using the same laser device as the device for the laser for forming the slits S 4  and S 5  in step S 38 . With this configuration, it is not necessary to separately provide a structure for forming the insulating groove  20 , and there is another advantage that the manufacturing cost of the photovoltaic device  200  can be reduced. 
     In addition, a step for removing the outer periphery portion of the photovoltaic device  200  or the like may be provided after step S 40 . Alternatively, a step for forming a back sheet or a resin layer for protecting the surface of the photovoltaic device  200  may be provided after step S 40 . The back sheet and the resin layer function as a protective layer of the photovoltaic device  200 .