Patent Publication Number: US-2013247969-A1

Title: Solar cell and method of manufacturing the same

Description:
BACKGROUND 
     1. Field 
     One or more embodiments relate to solar cells and methods of manufacturing the same, and more particularly, to a solar cell capable of preventing deterioration of a power generating efficiency by a shunt, and a method of manufacturing the solar cell. 
     2. Description of the Related Art 
     Recently, as existing energy resources, e.g., oil and coal, are expected to be exhausted, interest in alternative energies for replacing existing energy resources has risen. Among the alternative energies, solar cells are drawing attention as next generation batteries that directly change sunlight energy into electric energy by using semiconductor devices. 
     For example, a building-integrated photovoltaic (BIPV) system, i.e., a system using solar cells as envelop finishing materials or windows and doors of buildings, is used as an energy reduction measure and as power generating efficiency of solar cells. In the BIPV system, translucency and photoelectric conversion efficiency of solar cells are important, since the solar cells are required to perform as envelop finishing materials and power supplies via self-power generation. 
     SUMMARY 
     One or more embodiments include solar cells capable of preventing deterioration of a power generating efficiency by a shunt, and methods of manufacturing the same. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     According to one or more embodiments, a solar cell includes a rear electrode layer disposed on a substrate, the rear electrode layer being divided into a plurality of portions by a first separation groove, a light absorption layer and a buffer layer disposed on the rear electrode layer, the light absorption layer and buffer layer being divided into a plurality of portions by a second separation groove parallel to the first separation groove, a translucent electrode layer disposed on the buffer layer, the translucent electrode layer being divided into a plurality of portions by a third separation groove parallel to the first and second separation grooves, a light transmission unit exposing a portion of the substrate, the light transmission unit being defined by an opening through the rear electrode layer, the light absorption layer, the buffer layer, and the translucent electrode layer, and first and second insulation grooves at respective first and second sides of the light transmission unit, the first and second insulation grooves being perpendicular to the first through third separation grooves. 
     The light transmission unit may be disposed between the second and third separation grooves. 
     A length of each of the first and second insulation grooves along a first direction may be equal to or greater than a width of the light transmission unit along the first direction. 
     The first and second insulation grooves may contact the third separation groove. 
     The first and second insulation grooves may extend from the translucent electrode layer to a top surface of the rear electrode layer. 
     The first and second insulation grooves and the light transmission unit may be integrally formed. 
     The third separation groove and the light transmission unit may be integrally formed. 
     The rear electrode layer may include molybdenum (Mo). 
     The light absorption layer may include at least one of copper (Cu), indium (In), germanium (Ge), and selenium (Se). 
     According to one or more embodiments, a method of manufacturing a solar cell includes forming a rear electrode layer on a substrate, and forming a first separation groove dividing the rear electrode layer by performing a first patterning; forming a light absorption layer and a buffer layer on the rear electrode layer, forming a second separation groove dividing the light absorption layer and buffer layer by performing a second patterning, forming a translucent electrode layer on the buffer layer, and forming a third separation groove defining a plurality of photoelectric units by performing a third patterning, forming a light transmission unit by removing parts of the rear electrode layer, the light absorption layer, buffer layer, and the translucent electrode layer, and forming a pair of insulation grooves respectively at two sides of the light transmission unit, wherein the pair of insulation grooves are formed perpendicular to the first through third separation grooves that are parallel to each other. 
     The light transmission unit may be formed between the second and third separation grooves. 
     The first and second insulation grooves may be formed to contact the third separation groove. 
     The first and second insulation grooves and the third separation groove may be formed by removing parts of the translucent electrode layer, buffer layer, and light absorption layer. 
     The first and second insulation grooves and the light transmission unit may be integrally formed. 
     The light transmission unit and the third separation groove may be integrally formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features will become apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings, in which: 
         FIG. 1  illustrates a plan view of a solar cell according to an embodiment; 
         FIG. 2  illustrates a cross-sectional view taken along line I-I′ of  FIG. 1 ; 
         FIG. 3  illustrates a cross-sectional view taken along line II-II′ of  FIG. 1 ; 
         FIG. 4  illustrates a plan view of a solar cell according to another embodiment; 
         FIG. 5  illustrates a magnified view of a region A of  FIG. 4 ; 
         FIG. 6  illustrates a plan view of a solar cell according to another embodiment; 
         FIG. 7  illustrates a cross-sectional view taken along line of  FIG. 6 ; 
         FIG. 8  illustrates a cross-sectional view taken along line IV-IV′ of  FIG. 6 ; 
         FIG. 9  illustrates a magnified view of a region B of  FIG. 6 ; and 
         FIGS. 10 through 13  illustrate cross-sectional views of stages in a method of manufacturing a solar cell according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Korean Patent Application No. 10-2012-0028954, filed on Mar. 21, 2012, in the Korean Intellectual Property Office, and entitled: “Solar Cell and Method of Manufacturing the Same,” is incorporated by reference herein in its entirety. 
     Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     In the drawing figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. It will also be understood that when a layer, i.e., an element, is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout. 
       FIG. 1  is a plan view of a solar cell  100  according to an embodiment,  FIG. 2  is a cross-sectional view taken along line I-I′ of  FIG. 1 , and  FIG. 3  is a cross-sectional view taken along line II-II′ of  FIG. 1 . Here,  FIG. 1  illustrates the solar cell  100  on an x-y plane viewed from a z-direction,  FIG. 2  illustrates the solar cell  100  on an x-z plane viewed from a y-direction, and  FIG. 3  illustrates the solar cell  100  on a y-z plane viewed from an x-direction. 
     Referring to  FIGS. 1 through 3 , the solar cell  100  according to the current embodiment may include a substrate  110 , a rear electrode layer  120  disposed on the substrate  110  and divided by a first separation groove P 1 , a light absorption layer  130  and a buffer layer  140  disposed on the rear electrode layer  120  and divided by a second separation groove P 2 , a translucent electrode layer  150  disposed on the buffer layer  140  and divided by a third separation groove P 3 , and a light transmission unit  160  formed by removing parts of the rear electrode layer  120 , the light absorption layer  130 , buffer layer  140 , and the translucent electrode layer  150 . Also, the solar cell  100  may further include a pair of insulation grooves G 1  and G 2  respectively at two sides of the light transmission unit  160 . 
     The substrate  110  may be, e.g., a glass substrate having excellent light translucency or a polymer substrate. For example, the glass substrate may be formed of soda-lime glass or high strained point soda glass, and the polymer substrate may be formed of polyimide, but are not limited thereto. In another example, the glass substrate may be formed of low iron tempered glass protecting internal devices from external shock and containing a low amount iron to increase a transmittance of sunlight. Examples of low iron tempered glass may include soda-lime glass with low amount of iron, where sodium (Na) ions are extracted from the glass at a process temperature higher than 500° C. to increase efficiency of the light absorption layer  130  formed of Copper-Indium-Gallium-Selenide (CIGS). 
     The rear electrode layer  120  may be formed of a metal exhibiting excellent conductivity and excellent light reflectivity, e.g., molybdenum (Mo), aluminum (Al), and/or copper (Cu), such that charges formed by a photoelectric effect are collected and re-absorbed by the light absorption layer  130  by reflecting light that penetrates through the light absorption layer  130 . For example, the rear electrode layer  120  may include Mo to provide high conductivity, an ohmic-contact with the light absorption layer  130 , and high temperature stability under a selenium (Se) atmosphere. 
     The rear electrode layer  120  may have a thickness from about 200 nm to about 500 nm along the z-axis, and may be divided into a plurality of portions by the first separation groove P 1 . The first separation groove P 1  may be a groove parallel to one direction of the substrate  110 , e.g., along the x-axis. For example, the first separation groove P 1  may extend through the entire thickness of the rear electrode layer  120  along the z-axis to expose a portion of the substrate  110 . 
     The rear electrode layer  120  may be doped with alkali ions, e.g., Na ions. For example, while growing the light absorption layer  130  formed of CIGS on the rear electrode layer  120 , the alkali ions doped in the rear electrode layer  120  are mixed with the light absorption layer  130 , thereby having a structurally favorable effect on the light absorption layer  130  and improving conductivity of the light absorption layer  130 . Accordingly, a stand-off ratio Voc of the solar cell  100  is increased, and thus, an efficiency of the solar cell  100  may be improved. 
     Also, the rear electrode layer  120  may be formed of multiple films along the z-axis so as to obtain resistance characteristics of a contact surface with the substrate  110  and the rear electrode layer  120 . 
     The light absorption layer  130  is formed of a CIGS-based compound, e.g., the light absorption layer  130  may consist essentially of CIGS, to form a P-type semiconductor layer and to absorb incident sunlight. The light absorption layer  130  may be formed on the rear electrode layer  120  and in the first separation groove P 1  separating the rear electrode layer  120 , i.e., the light absorption layer  130  may contact the substrate  110  through the first separation groove P 1 . The light absorption layer  130  may have a thickness from about 0.7 μm to about 2 μm. 
     The buffer layer  140  may be formed on the light absorption layer  130  and may reduce a band gap difference between the light absorption layer  130  and the translucent electrode layer  150  to be described below. Further, the buffer layer  140  reduces recombination of holes and electrons that may be generated between the light absorption layer  130  and the translucent electrode layer  150 . The buffer layer  140  may be formed of, e.g., cadmium sulfide (CdS), zinc sulfide (ZnS), indium sulfide (In 2 S 3 ), and/or zinc magnesium oxide (Zn x Mg( 1-x )O). 
     The light absorption layer  130  and the buffer layer  140  may be divided into a plurality of portions by the second separation groove P 2 . The second separation groove P 2  may be a groove parallel to the first separation groove P 1  at a different location from the first separation groove P 1 . The second separation groove P 2  may extend thorough an entire combined thickness of the light absorption layer  130  and the buffer layer  140  along the z-axis to expose a top surface of the rear electrode layer  120 . 
     The translucent electrode layer  150  may be formed on the buffer layer  140 , so the translucent electrode layer  150  and the light absorption layer  130  form a P-N junction. Also, the translucent electrode layer  150  is formed of a transparent conductive material, e.g., boron-doped zinc oxide (ZnO:B), indium tin oxide (ITO), or indium zinc oxide (IZO), so as to capture charges formed by a photoelectric effect. Also, although not shown in  FIGS. 1 through 3 , a top surface of the translucent electrode layer  150  may be textured so as to reduce reflection of incident sunlight and increase light absorption by the light absorption layer  130 . 
     The translucent electrode layer  150  may be formed in the second separation groove P 2  to contact the rear electrode layer  120  exposed by the second separation groove P 2 . Therefore, the translucent electrode layer  150  may electrically connect the light absorption layer  130 , i.e., the plurality of portions of the light absorption layer  130 , by the second separation groove P 2 . In other words, two adjacent portions of the light absorption layer  130  along the y-axis may be on, e.g., directly on, a same portion of the rear electrode layer  120 . The translucent electrode layer  150  may contact the same portion of the rear electrode layer  120  through the second separation groove P 2 , i.e., between the two adjacent portions of the light absorption layer  130 . 
     The translucent electrode layer  150  may be divided into a plurality of portions by the third separation groove P 3  formed at a different location from the first and second separation grooves P 1  and P 2 . The third separation groove P 3  may be a groove parallel to the first and second separation grooves P 1  and P 2 , and may extend to a top surface of the rear electrode layer  120 , thereby forming a plurality of first through nth photoelectric units C 1  through Cn. 
     An insulation material, e.g., air, may be charged in the third separation groove P 3  so as to form an insulation layer between the first through nth photoelectric units C 1  through Cn. Thus, the first through nth photoelectric units C 1  through Cn may be connected in series in a transverse direction of  FIG. 1 , e.g., along the y-axis, perpendicular to the third separation groove P 3 , e.g., along the x-axis. 
     The light transmission unit  160  may be formed at a location where the parts of the rear electrode layer  120 , the light absorption layer  130 , the buffer layer  140 , and the translucent electrode layer  150  are removed. In other words, as illustrated in  FIGS. 2-3 , a portion of the rear electrode layer  120 , the light absorption layer  130 , the buffer layer  140 , and the translucent electrode layer  150  may be removed to define an opening, i.e., the light transmission unit  160 , exposing a top surface of the substrate  110 . 
     In  FIG. 1 , the light transmission unit  160  is formed in the transverse direction, e.g., along the y-axis. For example, each light transmission unit  160  may extend continuously along the y-axis to transverse the first through nth photoelectric units C 1  through Cn, and a plurality of light transmission units  160  may be spaced apart from each other along the x-axis. In this case, the first through nth photoelectric units C 1  through Cn connected in series in the transverse direction may form a plurality of arrays L 1  through Ln in a longitudinal direction, e.g., along the x-axis, and the arrays L 1  through Ln may be connected in parallel. 
     As shown in  FIG. 2 , the pair of insulation grooves G 1  and G 2  may be formed respectively on two sides of the light transmission unit  160 . In other words, the light transmission unit  160  may be positioned between the insulation grooves G 1  and G 2  in the x-axis direction. The insulation grooves G 1  and G 2  are perpendicular to the first through third separation grooves P 1  through P 3 , which are parallel to each other, and extend to the top surface of the rear electrode layer  120 . For example, the first through third separation grooves P 1  through P 3  may extend along the x-axis, while the insulation grooves G 1  and G 2  may extend along the y-axis and may expose the top surface of the rear electrode layer  120 . 
     Accordingly, the first through nth photoelectric units C 1  through Cn connected in series may be electrically separated from an inner surface of the light transmission unit  160  in the x-direction of  FIG. 1 . For example, as illustrated in  FIG. 1 , the first through nth photoelectric units C 1  through Cn in the first array L 1  may be separated from the first light transmission unit  160  along the x-axis by the insulation groove G 1 . Similarly, the first through nth photoelectric units C 1  through Cn in the second array L 2  may be separated from the first and second light transmission unit  160  along the x-axis by the respective insulation grooves G 1  and G 2 . As such, the first through nth photoelectric units C 1  through Cn are separated from potential conductive residue in the light transmission unit  160 , thereby improving efficiency of the solar cell  100 . 
     In detail, as the light transmission unit  160  may be formed via a laser scribing process, conductive material of the translucent electrode layer  150  evaporated by a laser beam during the laser scribing process may be re-deposited inside of the light transmission unit  160 . The re-deposited conductive material inside the light transmission unit  160  may potentially form a shunt path, thereby decreasing efficiency of the solar cell  100 . However, as according to example embodiments, the first through nth photoelectric units C 1  through Cn are separated from the light transmission unit  160 , i.e., where the shunt path may be generated, by insulating grooves, efficiency of the solar cell  100  may not be affected, i.e., efficiency may be prevented from decreasing due to the shunt path. 
     As shown in  FIG. 3 , the light transmission unit  160  may be disposed between the second and third separation grooves P 2  and P 3 . Here, the second and third separation grooves P 2  and P 3  do not only denote the second and third separation grooves P 2  and P 3  adjacent to each other, but may denote the second and third separation grooves P 2  and P 3  disposed in the first through nth photoelectric units C 1  through Cn. However, based on  FIG. 1  where the first through third separation grooves P 1  through P 3  are formed while moving in the y-direction, when the light transmission unit  160  is formed between the second and third separation grooves P 2  and P 3 , the third separation groove P 3  may be on the right, i.e., in the y-direction, with respect to the second separation groove P 2 . 
     As such, when the light transmission unit  160  is disposed between the second and third separation grooves P 2  and P 3 , the light transmission unit  160  is disposed inside a non-power generation region D. Accordingly, even if a conductive material is re-deposited in the light transmission unit  160  disposed in the y-direction of  FIG. 1  while performing the laser scribing process to form the light transmission unit  160 , the solar cell  100  is not affected by the shunt path. 
     Lengths of the insulation grooves G 1  and G 2  along the y-axis may be equal to or greater than a width of the light transmission unit  160  along the y-axis. The insulation grooves G 1  and G 2  may contact the third separation groove P 3 , as will be described below with reference to  FIGS. 4 and 5 . 
     Referring back to  FIG. 2 , a width W 1  of the insulation grooves G 1  and G 2  along the x-axis may be from about 30 μm to about 90 μm considering a decrease in a power generation region of the solar cell  100 . A distance W 2  between the insulation grooves G 1  and G 2  and the light transmission unit  160  along the x-axis may be from about 10 μm to about 30 μm, but are not limited thereto. For example, as described below, the insulation grooves G 1  and G 2  and the light transmission unit  160  may be continuously formed, i.e., the distance W 2  may be 0. 
       FIG. 4  is a plan view of a solar cell  200  according to another embodiment.  FIG. 5  is a magnified view of a region A of  FIG. 4 . 
       FIG. 4  shows a light transmission unit  260  formed throughout every two photoelectric units. In other words, adjacent light transmission units  260  along the y-axis may be separated from each other. For example, first and second photoelectric units C 1  and C 2  where the light transmission unit  260  is formed are connected in series in a transverse direction, and form a plurality of arrays L 1  through Lm connected in parallel in a longitudinal direction. Similarly, fourth and fifth photoelectric units C 4  and C 5  or n−1th and nth photoelectric units Cn−1 and Cn form a plurality of arrays connected in parallel in the longitudinal direction. Accordingly, based on a location of the light transmission unit  260 , the first through nth photoelectric units C 1  through Cn may be connected in series, parallel, or both in series and parallel. 
     As described above with reference to  FIGS. 1 through 3 , the solar cell  200  of  FIG. 4  may also include a pair of insulation grooves G 1  and G 2  respectively at two sides of the light transmission unit  260 , so as to prevent an efficiency decrease of the solar cell  200  due to a shunt path that may be generated inside of the light transmission unit  260 . Here, lengths of the insulation grooves G 1  and G 2  may be equal to or greater than a width of the light transmission unit  260  parallel to a length direction of the insulation grooves G 1  and G 2 , thereby decreasing an effect of the shunt path that may be generated within the light transmission unit  260 . 
     Also, as shown in  FIG. 4 , the light transmission unit  260  may overlap a plurality of second and third separation grooves P 2  and P 3 , and may be disposed between the pair of insulation grooves G 1  and G 2 . For example, as further illustrated in  FIG. 4 , two third separation grooves P 3  and one second separation groove P 2  may define each photoelectric unit. As shown in  FIG. 5 , the pair of insulation grooves G 1  and G 2  may connect with the third separation groove P 3 . 
     For example, when the light transmission unit  260  is formed throughout the fourth and fifth photoelectric cells C 4  and C 5 , the pair of insulation grooves G 1  and G 2  formed respectively on two sides of the light transmission unit  260  cross the two third separation grooves P 3  defining the fourth photoelectric cell C 4 , and thus, the fourth photoelectric cell C 4  is not affected by a shunt formed inside of the light transmission unit  260 . 
     One third separation groove P 3  from among the two third separation grooves P 3  defining the fifth photoelectric cell C 5  is the same third separation groove P 3  when the light transmission unit  260  is disposed between the second and third separation grooves P 2  and P 3 . Therefore, the inside of the light transmission unit  260  and a power generation region of the solar cell  200  are definitely separated from each other by forming the insulation grooves G 1  and G 2  to contact the third separation groove P 3  in the y-direction from among the two third separation grooves P 3  defining the fifth photoelectric cell C 5 , as shown in  FIG. 5 . 
     However, when the light transmission unit  260  is disposed between the second and third separation grooves P 2  and P 3 , the insulation grooves G 1  and G 2  respectively at two sides of the light transmission unit  260  may not contact the second separation groove P 2 . This is because, since a region between the second and third separation grooves P 2  and P 3  is a non-power generation region and the second separation groove P 2  electrically connects the translucent electrode layer  150  and the rear electrode layer  120 , a power generating efficiency of the solar cell  200  is not affected even if a shunt is generated inside of the light transmission unit  260  near the second separation groove P 2 . 
       FIG. 6  is a plan view of a solar cell  300  according to another embodiment.  FIG. 7  is a cross-sectional view taken along line of  FIG. 6 ,  FIG. 8  is a cross-sectional view taken along line IV-IV′ of  FIG. 6 , and  FIG. 9  is a magnified view of a region B of  FIG. 6 . 
     First, referring to  FIGS. 6 through 8 , the solar cell  300  according to the current embodiment may include a substrate  310 , a rear electrode layer  320  divided by a first separation groove P 1 , a light absorption layer  330  and a buffer layer  340  divided by a second separation groove P 2 , a translucent electrode layer  350  divided by a third separation groove P 3 , and a light transmission unit  360 . The light transmission unit  360  may include a pair of insulation grooves G 1  and G 2  respectively at two sides of the light transmission unit  360 . Also, the light transmission unit  360  may be disposed between the second and third separation grooves P 2  and P 3  along the y-axis, and the insulation grooves G 1  and G 2  may contact the third separation groove P 3 . 
     Since the substrate  310 , the rear electrode layer  320 , the light absorption layer  330 , the buffer layer  340 , the translucent electrode layer  350 , and the light transmission unit  360  are respectively identical to the substrate  110 , the rear electrode layer  120 , the light absorption layer  130 , the buffer layer  140 , the translucent electrode layer  150 , and the light transmission unit  160 , repeated descriptions thereof are not provided. 
     In the solar cell  300  of  FIG. 6 , each first through nth photoelectric unit C 1  through Cn includes the light transmission unit  360  formed in a longitudinal direction. Also, in  FIG. 7 , the pair of insulation grooves G 1  and G 2  and the light transmission unit  360  may be integrally formed, e.g., formed as a single opening where the insulation grooves G 1  and G 2  and light transmission unit  360  are in fluid communication, and in  FIG. 8 , the third separation groove P 3  and the light transmission unit  360  may be integrally formed. 
     As such, when the light transmission unit  360  contacts the pair of insulation grooves G 1  and G 2  and/or the third separation groove P 3 , an efficiency of the solar cell  300  may be increased as a non-power generation region in the solar cell  300  is decreased, as shown in  FIG. 9 . 
       FIGS. 10 through 13  are cross-sectional views of stages in a method of manufacturing a solar cell according to an embodiment. The method of  FIGS. 10 through 13  is one of manufacturing the solar cell  100  of  FIGS. 1 through 3 , but the method may also be applied to the solar cells  200  and  300  of  FIGS. 4 through 9 . 
     Referring to  FIG. 10 , the rear electrode layer  120  may be formed on the substrate  110 . Then, the rear electrode layer  120  may be divided into a plurality of portions by performing a first patterning, as shown in  FIG. 10 . 
     For example, the rear electrode layer  120  may be formed by coating a conductive paste on the substrate  110  and then performing a thermal process. In another example, the rear electrode layer  120  may be formed by a plating process. In yet another example, the rear electrode layer  120  may be formed via a sputtering process, e.g., using a Mo target. 
     The first patterning may be performed via a laser scribing process to form the first separation groove P 1 . The laser scribing process is a process of evaporating some of the rear electrode layer  120  by irradiating a laser beam towards the substrate  110  from a bottom of the substrate  110 . The first separation groove P 1  divides the rear electrode layer  120  at regular intervals, e.g., the rear electrode layer  120  may be divided into a plurality of discrete portions spaced apart from each other at a constant interval. 
     Next, as shown in  FIG. 11 , the light absorption layer  130  and the buffer layer  140  may be formed, followed by a second patterning is performed. 
     For example, the light absorption layer  130  may be formed by using a co-evaporation method wherein Cu, In, Ga, and Se are put into a small electric furnace installed in a vacuum chamber, and are heated for vacuum deposition. In another example, the light absorption layer  130  may be formed by a sputtering/selenization method, where a CIG-based metal precursor film is formed on the rear electrode layer  120  by using a Cu target, an In target, and a Ga target, and then the CIG-based metal precursor film is thermally treated under a hydrogen selenide (H 2 Se) gas atmosphere, such that the CIG-based metal precursor film reacts with Se to form a CIGS-based light absorption layer. In another example, the light absorption layer  130  may be formed by using an electro-deposition method or a molecular organic chemical vapor deposition (MOCVD) method. 
     The buffer layer  140  reduces a band gap difference between the light absorption layer  130  of a P-type and the translucent electrode layer  150  of an N-type, and reduces re-combination of electrons and holes that may be generated on an interface between the light absorption layer  130  and the translucent electrode layer  150 . The buffer layer  140  may be formed via, e.g., a chemical bath deposition (CBD) method, an atomic layer deposition (ALD) method, or an ion lay gas reaction (ILGAR) method. 
     After forming the light absorption layer  130  and the buffer layer  140 , the second patterning is performed. For example, the second patterning may be performed via mechanical scribing, where the second separation groove P 2  may be formed by moving a sharp object, e.g., a needle, in a direction parallel to the first separation groove P 1  to a location spaced apart from the first separation groove P 1 . In another example, the second patterning may be performed by using a laser beam. 
     The second patterning divides the light absorption layer  130  into a plurality of portions, and the second separation groove P 2  formed via the second patterning extends to a top surface of the rear electrode layer  120  to expose the rear electrode layer  120 . 
     Next, as shown in  FIG. 12 , after forming the translucent electrode layer  150 , a third patterning is performed. 
     The translucent electrode layer  150  may be formed of a transparent conductive material, e.g., ZnO:B, ITO, or IZO, by using an MOCVD method, a low-pressure chemical vapor deposition (LPCVD) method, or a sputtering method. The translucent electrode layer  150  is also formed in the second separation groove P 2 , thereby electrically connecting the light absorption layers  130  divided by the second separation groove P 2 . 
     The third patterning may be performed via a mechanical scribing method, and the third separation groove P 3  formed via the third patterning may extend to a top surface of the rear electrode layer  120  to form a plurality of photoelectric units. Also, an insulation layer may be formed by charging air in the third separation groove P 3 . 
     Although not shown in  FIG. 12 , a top surface of the translucent electrode layer  150  may be textured. Here, texturing denotes forming a ribbed pattern on a surface via a physical or chemical method. As such, when the top surface of the translucent electrode layer  150  is rough via texturing, reflectivity of an incident light is reduced, and thus, an amount of captured light may be increased. Accordingly, optical loss may be reduced. 
     Next, as shown in  FIG. 13 , parts of the rear electrode layer  120 , the light absorption layer  130 , the buffer layer  140 , and the translucent electrode layer  150  are removed to form the light transmission unit  160 . Also, after forming the light transmission unit  160 , the pair of insulation grooves G 1  and G 2  are respectively formed at two sides of the light transmission unit  160 , as shown in  FIGS. 1 and 2 . 
     The parts of the rear electrode layer  120 , the light absorption layer  130 , the buffer layer  140 , and the translucent electrode layer  150  may be removed via a laser scribing method using a laser having a wavelength from about 1060 nm to about 1064 nm, a pulse width from about 10 ns to about 100 nm, and power from about 0.5 W to about 20 W, but is not limited thereto. Here, the light transmission unit  160  may be formed between the second and third separation grooves P 2  and P 3 . Furthermore, as shown in  FIG. 8 , the light transmission unit  160  may contact the third separation groove P 3 . 
     The insulation grooves G 1  and G 2  of  FIG. 2  may be formed to expose the top surface of the rear electrode layer  120  via a mechanical scribing method. Accordingly, an efficiency of the solar cell  100  may be prevented from being deteriorated by a shunt path that may be generated while forming the light transmission unit  160 . Further, as shown in  FIG. 7 , the insulation grooves G 1  and G 2  may contact the light transmission unit  360 , thereby reducing a non-power generation region. 
     As described above, according to the one or more of the above embodiments, deterioration of a power generating efficiency of a solar cell, e.g., due to a shunt generated while forming a light transmission unit, may be prevented. Also, the light transmission unit may be formed to contact a pair of insulation grooves and/or a third separation groove, thereby reducing a non-power generation region of the solar cell. 
     In contrast, in a conventional solar cell, e.g., used in the BIPV system, a light transmission unit is formed by performing a laser scribing process. However, as described previously, the laser scribing process may cause a conductive material (for example, a transparent conducting oxide (TCO)-based translucent electrode layer) may be re-deposited at a side, e.g., an inner surface, of the light transmission unit, thereby forming a shunt resistance path, i.e., an unnecessary current path. Such a shunt in the conventional solar cell may reduce the power generating efficiency of the solar cell. 
     The solar cells according to one or more embodiments are not limited to the structures and methods described above, and all or some of the embodiments may be selectively combined for various modifications. 
     Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. In some instances, as would be apparent to one of ordinary skill in the art as of the filing of the present application, features, characteristics, and/or elements described in connection with a particular embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise specifically indicated. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope of the embodiments as set forth in the following claims.