Patent Publication Number: US-2013240010-A1

Title: Solar cell and manufacturing method thereof

Description:
RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2012-0025759 filed in the Korean Intellectual Property Office on Mar. 13, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Example embodiments relate to a solar cell and/or a manufacturing method thereof. 
     2. Description of the Related Art 
     Fossil fuels, such as coal and petroleum, are used as energy sources. However, fossil fuels are being exhausted and cause global warming and environmental pollution. Solar light, tidal power, wind power, geothermal heat and the like are being studied as an alternative energy sources for replacing fossil fuel. 
     Among them, technology of converting solar light into electricity takes the lead. Various materials and devices are being developed for solar cells that convert solar light into electricity. Solar cells may have a multi-layered p-n junction structure and may include III-V Group materials. 
     The above-described technology may use specific wavelength of solar light among various wavelengths. A multi-junction structure may be applied to use several wavelengths. Techniques for using the currents generated by multi-junction solar cells are being studied. 
     SUMMARY 
     Example embodiments relate to a solar cell and/or a manufacturing method thereof. 
     According to example embodiments, a solar cell includes a transparent base substrate having a first surface and a second surface opposite the first surface, a first photoelectric layer having a thin film shape on the first surface of the base substrate, and a second photoelectric layer having a thin film shape on the second surface of the base substrate. The second photoelectric layer has a different bandgap than a bandgap of the first photoelectric layer. 
     The first surface may be under the second surface, and the bandgap of the first photoelectric layer may be smaller than the bandgap of the second photoelectric layer. 
     The solar cell may further include first and second terminals connected to the first photoelectric layer, and third and fourth terminals connected to the second photoelectric layer. The first photoelectric layer may be between the base substrate and the first and second terminals. The second photoelectric layer may be between the base substrate and the third and fourth terminals. 
     The first photoelectric layer may include first and second impurity regions connected to the first and second terminals, respectively, and the second photoelectric layer may include third and fourth impurity regions connected to the third and fourth terminals, respectively. The first and second impurity regions may have opposite conductivities. The third and fourth impurity regions may have opposite conductivities. 
     The solar cell may further include a passivation layer between the substrate and the first photoelectric layer. 
     The solar cell may further include a wavelength conversion member between the base substrate and the first photoelectric layer. The wavelength conversion member may be configured to change a wavelength of incident light. 
     The wavelength conversion member may include a pattern on the substrate. 
     The wavelength conversion member may include nanoparticles. 
     The base substrate may include an insulator, for example, at least one of glass, quartz, and plastic. 
     The base substrate may have a thickness from about 50 microns to about 10 centimeters. 
     According to example embodiments, a method of manufacturing a solar cell includes forming a first photoelectric layer by thin film deposition on a first surface of a transparent insulating base substrate, forming a second photoelectric layer by thin film deposition on a second surface of the base substrate. The second photoelectric layer may have a different bandgap than a bandgap of the first photoelectric layer. The first surface and the second surface of the base substrate may be opposite to each other. The method may further include forming a first electrode on the first photoelectric layer opposite the base substrate, and forming a second electrode on the second photoelectric layer opposite the base substrate. 
     The first surface may be under the second surface, and the bandgap of the first photoelectric layer may be less than the bandgap of the second photoelectric layer. 
     The method may further include forming a plurality of impurity regions by implanting impurities in the first and second photoelectric layers. 
     The method may further include forming a passivation layer between the base substrate and the first photoelectric layer. 
     The method may further include forming a wavelength conversion member between the base substrate and the first photoelectric layer. The wavelength conversion member may be configured to change wavelength of incident light. 
     Forming the wavelength conversion member may include forming a pattern on the base substrate. 
     Forming the wavelength conversion member may include forming nanoparticles on the base substrate. 
     The base substrate may include at least one of glass, quartz, and plastic. 
     The base substrate may have a thickness from about 50 microns to about 10 centimeters. 
     The thin film deposition may include one of chemical deposition and physical deposition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of example embodiments will be apparent from the more particular description of non-limiting embodiments of inventive concepts, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of example embodiments. In the drawings: 
         FIG. 1  is a schematic sectional view of a solar cell according to example embodiments. 
         FIGS. 2 and 3  are schematic sectional views illustrating a method of manufacturing the solar cell according to example embodiments. 
         FIGS. 4 ,  5 ( a ),  5 ( b ), and  6 ( a ) to  6 ( h ) are schematic sectional views of solar cells according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings, in which some example embodiments are shown. Example embodiments, may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of example embodiments of inventive concepts to those of ordinary skill in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements, and thus their description may be omitted. In the drawing, parts having no relationship with the explanation are omitted for clarity 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items. Other words used to describe the relationship between elements or layers should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” “on” versus “directly on”). 
     It will be understood that, although the terms “first”, “second”, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of example embodiments. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including,” if used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof. 
     Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle may have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, such as those defined in commonly-used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     A solar cell and a manufacturing method thereof according to example embodiments are described in detail with reference to  FIGS. 1 to 3 . 
       FIG. 1  is a schematic sectional view of a solar cell according to example embodiments, and  FIGS. 2 and 3  are schematic sectional views illustrating a method of manufacturing the solar cell according to example embodiments. 
     A solar cell  100  according to example embodiments includes a transparent supporting base substrate  110 , a lower photoelectric layer  120  and an upper photoelectric layer  130  that are deposited on lower and upper surfaces of the supporting substrate  110 , respectively, and a plurality of terminals  140 ,  150 ,  160  and  170  connected to the lower and upper photoelectric layers  120  and  130 . 
     The base substrate  110  may include an insulator electrically separating the lower photoelectric layer  120  and the upper photoelectric layer  130 . The base substrate  110  may include a transparent substrate having a degree of strength, for example, glass, quartz, or plastic substrate so that the lower and upper photoelectric layers  120  and  130  may be deposited on the lower and upper surfaces of the base substrate  110  in forms of thin films. The thickness of the base substrate  110  may be about 50 microns (μm) to dozens of centimeters, but example embodiments are not limited thereto. If the base substrate  110  is a plastic, the base substrate  110  may include at least one of polyester, polyethylene, polyethersulfone (PES), polyamide, and polyimide, but example embodiments are not limited thereto. 
     The lower and upper photoelectric layers  120  and  130  may generate electricity upon receipt of light, and may have different energy bandgaps. For example, the bandgap of the upper photoelectric layer  130  may be greater than that of the lower photoelectric layer  120 , and the difference in the bandgap between the lower photoelectric layer  120  and the upper photoelectric layer  130  may be about 0.3 to about 0.8 eV. If the bandgap difference between the photoelectric layers  120  and  130  is lower than 0.3 eV or greater than 0.8 eV, an available wavelength range of light may decrease or an output voltage may be less (and/or an output voltage may not be optimized), thereby reducing the efficiency of power generation. The bandgap of the lower photoelectric layer  120  may be about 0.4 eV to about 1.5 eV, and/or 0.5 eV to about 1.5 eV, while the bandgap of the upper photoelectric layer  130  may be about 1.0 eV to about 2.5 eV and/or about 1.0 eV to about 2.3 eV. 
     Examples of materials for the photoelectric layers  120  and  130  include various polymers and semiconductors that may be deposited in thin films, such as Si, Ge, Cu—In—Ga—Se (CIGS), CdTe, GaSb, InAs, PbS, GaP, ZnTe, CdS, AlP, and/or GaAs, but example embodiments are not limited thereto. Polycrystalline or single-crystalline silicon (Si) may have a bandgap of about 1.1 eV to about 1.2 eV, while amorphous silicon may have a higher bandgap of about 1.6 eV to about 1.7 eV. Germanium (Ge) may have a bandgap of about 0.6 eV to about 0.7 eV, and CdTe and GaAs may have a bandgap of about 1.4 eV to about 1.5 eV. GaSb may have a bandgap of about 0.7 eV, and InAs and PbS may have a bandgap of about 0.4 eV. GaP and ZnTe may have bandgap of about 2.2 eV to about 2.3 eV, and CdS and AlP may have bandgap of about 2.4 eV to about 2.5 eV. CIGS may have a bandgap of about 1.0 to about 1.7 eV depending on the composition ratio of In and Ga. A CIGS that contains mainly In but substantially no Ga, i.e., that contains Cu—In—Se as main ingredients (hereinafter referred to as “CIS”) may have a bandgap of about 1.0 eV. On the contrary, a CIGS that contains mainly Ga but substantially no In, i.e., that contains Cu—Ga—Se as main ingredients (hereinafter referred to as “CGS”) may have a bandgap about 1.7 eV. Polymers are known to have bandgaps of equal to or greater than about 1.7 eV. 
     The above-described materials are classified into three groups according to the degree of the bandgap. The first group has a bandgap of about 1.0 eV to about 1.2 eV and may include crystalline silicon and CIS (Cu—In—Se), and the second group has a bandgap equal to or greater than about 1.4 eV and may include amorphous silicon, CGS, CdTe, GaAs, GaP, ZnTe, CdS, AlP, and polymer. The last group has a bandgap equal to or lower than about 0.7 eV and may include Ge, GaSb, InAs, and PbS. 
     Among the three groups, the second group may be used mainly for the upper photoelectric layer  130 , while the last group mainly for the lower photoelectric layer  120 . The first group may be used for either the lower photoelectric layer  120  or the upper photoelectric layer  130  as the case may be. However, the usage is not limited thereto, and each of the groups may be used either the lower photoelectric layer  120  or the upper photoelectric layer  130  depending on the relative degree of the bandgap. 
     For example, when crystalline silicon and CIS in the first group is used for the upper photoelectric layer  130 , Ge in the last group may be used for the lower photoelectric layer  120 . On the contrary, when crystalline silicon and CIS in the first group is used for the lower photoelectric layer  120 , amorphous silicon, CGS, CdTe, GaAs, GaP, ZnTe, CdS, AlP, and/or polymer may be used for the upper photoelectric layer  130 . In this case, amorphous silicon and CGS that have bandgaps of about 1.6 eV to about 1.8 eV may give higher efficiency than CdTe and GaAs that have relatively low bandgaps in the second group. 
     The lower and upper photoelectric layers  120  and  130  may be formed by thin film deposition, for example, chemical deposition such as chemical vapor deposition (CVD) or physical deposition such as sputtering. Each of the photoelectric layers  120  and  130  may be about 50 nm to about 100 μm. However, example embodiments are not limited thereto. 
     The plurality of terminals  140 ,  150 ,  160  and  170  include a pair of lower terminals  140  and  150  disposed under the lower photoelectric layer  120  and a pair of lower terminals  160  and  170  disposed on the upper photoelectric layer  130 . Therefore, the current flowing in each of the photoelectric layers  120  and  130  flows outward through respective terminals  140  and  150  or  160  and  170 . That is, the current in the lower photoelectric layer  120  flows outward through the lower terminals  140  and  150 , while that in the upper photoelectric layer  130  through the upper terminals  160  and  170 . However, since the lower photoelectric layer  120  and the upper photoelectric layer  130  are electrically isolated from each other, the current from the lower photoelectric layer  120  may not pass through the upper terminals  160  and  170 , and the current from the upper photoelectric layer  130  may not pass through the lower terminals  140  and  150 . 
     Each of the terminals  140 ,  150 ,  160  and  170  may include low-resistivity metal such as copper and silver, and may have a thickness of about 500 nm to about 2 μm. The lower terminals  140  and  150  may be as wide as possible in order to reduce outward light leakage, while the upper terminals  160  and  170  may be as narrow as possible in order to reduce the blocking of the light heading for the photoelectric layers  120  and  130 . For example, the width of each of the upper terminals  160  and  170  may be about 100 nm to about 1.5 μm. 
     According to example embodiments, a method of manufacturing the solar cell  100  is described with reference to  FIG. 2 . Referring to  FIG. 2 , a supporting base substrate  110  including at least one of transparent glass, quartz, and plastic is first prepared. 
     Thereafter, referring to  FIG. 3 , a lower photoelectric layer  120  and an upper photoelectric layer  130  are deposited on the base substrate  110  by thin film deposition, for example, one of CVD, or sputtering. 
     Finally, lower terminals  140  and  150  and upper terminals  160  and  170  are formed on the lower photoelectric layer  120  and the upper photoelectric layer  130 , respectively, as shown in  FIG. 1 . 
     In the above-described structure of the solar cell  100 , the magnitude of the current generated by the lower photoelectric layer  120  may be different from the magnitude of the current generated by the upper photoelectric layer  130 . In this case, if the upper photoelectric layer  130  and the lower photoelectric layer  120  are electrically connected to each other, a net current of the solar cell may be determined by a lower one of the currents generated by the upper photoelectric layer  130  and the lower photoelectric layer  120 . Therefore, an excess amount of the current generated by one of the photoelectric layers  120  and  130  may not be utilized, which may reduce the efficiency of the solar cell. However, solar cells according to example embodiments electrically separate the upper photoelectric layer  130  and the lower photoelectric layer  120  to collect the currents having different magnitudes generated by the upper photoelectric layer  130  and the lower photoelectric layer  120  to be used without current loss, thereby increasing the efficiency. 
     Furthermore, since the lower and upper photoelectric layers  120  and  130  are formed as thin films under and on the transparent supporting base substrate  110 , the manufacturing process may be simple and the manufacturing cost may be reduced. In particular, when using glass or plastic for the base substrate  110 , the manufacturing cost may be much reduced compared with a case that one of the lower and upper photoelectric layers  120  and  130  is a single crystalline silicon substrate. 
     Next, a solar cell according to example embodiments is described with reference to  FIG. 4 . 
       FIG. 4  is a schematic sectional view of a solar cell according to example embodiments. 
     Referring to  FIG. 4 , a solar cell  200  includes a supporting base substrate  210 , a lower photoelectric layer  220 , an upper photoelectric layer  230 , lower terminals  240  and  250 , and upper terminals  260  and  270 , like the solar cell  100  shown in  FIG. 1 . However, unlike the solar cell  100  shown in  FIG. 1 , the solar cell  200  further includes lower and upper passivation layers  280  and  290  disposed between the base substrate  210  and the lower and upper photoelectric layers  220  and  230 , respectively. 
     The passivation layers  280  and  290  may limit (and/or prevent) defects due to the direct contact between the base substrate  210  and the photoelectric layers  220  and  230 , for example, poor adhesion therebetween or contamination of the photoelectric layers  220  and  230 . The passivation layers  280  and  290  may include a dielectric material such as an oxide layer or a nitride layer having a thickness of about 1 nm to about 500 nm, or may include a semiconductor material such as an amorphous silicon layer having a thickness of about 0.5 nm to about 500 nm. For example, the passivation layers  280  and  290  may each independently include at least one of silicon oxide, silicon nitride, silicon oxynitride, and aluminum oxide. The passivation layers  280  and  290  include the same or different materials. 
     One of the lower and upper passivation layers  280  and  290  may be omitted. 
     Other portions of the solar cell  200  may be similar to corresponding portions shown in  FIG. 1 , and thus the detailed description thereof is omitted. 
     Next, a solar cell according to example embodiments is described in detail with reference to  FIGS. 5(   a ) and  5 ( b ). 
       FIG. 5(   a ) is a schematic sectional view of a solar cell according to example embodiments. 
     Referring to  FIG. 5(   a ), a solar cell  300   a  includes a supporting base substrate  310 , a lower photoelectric layer  320 , an upper photoelectric layer  330 , lower terminals  340  and  350 , and upper terminals  360  and  370 , like the solar cell  100  shown in  FIG. 1 . However, unlike the solar cell  100  shown in  FIG. 1 , the solar cell  300   a  further includes lower and upper wavelength conversion members  380  and  390  disposed between the base substrate  310  and the lower and upper photoelectric layers  320  and  330 , respectively. 
     The wavelength conversion members  380  and  390  may change the wavelength of incident light, for example, may convert light that may not be absorbed by the photoelectric layers  320  and  330  into light that may be absorbed by the photoelectric layers  320  and  330 . The wavelength conversion members  380  and  390  may be formed by forming patterns on surfaces of the base substrate  310 , or by depositing a metal such as gold or aluminum in forms of nanoparticles on the base substrate  310  to generate plasmons. Conversion of a desired range of wavelength into a wavelength range that may be absorbed by the photoelectric layers  320  and  330  may be realized by adjusting the size and the pitch of the wavelength conversion members  380  and  390 . 
     The wavelength conversion members  380  and  390  may include at least one of rare earth ions (e.g., Er+3, Tb+3, Tm+3, and Yb+3), transition metal ions (Zn, Pb, Ti, and Cd+), and nanocrystals (e.g., silicon quantum dots). However, example embodiments are not limited thereto. 
     One of the wavelength conversion members  380  and  390  may be omitted. 
     The solar cell  300   a  may further include the passivation layers  280  and  290  shown in  FIG. 4 . 
     Referring to  FIG. 5(   b ), a solar cell  300   b  according to example embodiments may include each feature of the solar cell  300   a  in  FIG. 5(   a ) and further include the passivation layers  280  and  290  shown in  FIG. 4 . In the solar cell  300   b  illustrated in  FIG. 5(   b ), one of the wavelength conversion members  380  and  390  may be omitted, and/or one of the passivation layers  280  and  290  may be omitted. 
     As described above, the solar cell  300  utilizes the wavelength conversion members  380  and  390  to make use of light with almost all ranges of wavelength in power generation, thereby increasing power generation efficiency. 
     Other portions of the solar cell  300  may be similar to corresponding portions shown in  FIG. 1 , and thus the detailed description thereof is omitted. 
     Next, solar cells according to example embodiments are described in detail with reference to  FIGS. 6(   a ) to  6 ( h ). 
       FIG. 6(   a ) is a schematic sectional view of a solar cell  400   a  according to example embodiments. 
     Referring to  FIG. 6(   a ), a solar cell  400   a  includes a transparent supporting base substrate  410 , a lower photoelectric layer  420 , an upper photoelectric layer  430 , lower terminals  440  and  450 , and upper terminals  460  and  470 , like the solar cell  100  shown in  FIG. 1 . 
     The lower photoelectric layer  420  includes a low-concentration impurity region  422  and a plurality of high-concentration impurity regions  424  and  426  that are disposed in the low-concentration impurity region  422  near a top surface and have impurity concentrations higher than the low-concentration impurity region  422 . Similarly, the upper photoelectric layer  430  includes a low-concentration impurity region  432  and a plurality of high-concentration impurity regions  434  and  436  that are disposed in the low-concentration impurity region  432  near a top surface and have impurity concentrations higher than the low-concentration impurity region  432 . 
     The low-concentration impurity regions  422  and  432  may include P-type or N-type impurity, and the low-concentration impurity region  422  of the lower photoelectric layer  420  and the low-concentration impurity region  432  of the upper photoelectric layer  430  may have opposite conductivities. 
     The high-concentration impurity regions  424 ,  426 ,  434  and  436  may be spaced apart from one another, and may be connected to corresponding lower and upper terminals  440 ,  450 ,  460  and  470 . Adjacent high-concentration impurity regions  424 ,  426 ,  434  and  436  may have opposite conductivities. 
     The high-concentration impurity regions  434  and  436  of the upper photoelectric layer  430  may be either large or small, and the large high-concentration impurity regions  434  and the small high-concentration impurity regions  436  may be alternately arranged. The large high-concentration impurity regions  434  may have a conductivity opposite to a conductivity of the small high-concentration impurity regions  436  and the low-concentration impurity region  432 . For example, when the low-concentration impurity region  432  includes P-type impurity of low concentration, the small high-concentration impurity region  436  may include P-type impurity of high concentration while the large high-concentration impurity region  434  may include N-type impurity of high concentration. On the contrary, when the low-concentration impurity region  432  includes N-type impurity of low concentration, the small high-concentration impurity region  436  may include N-type impurity of high concentration while the large high-concentration impurity region  434  may include P-type impurity of high concentration. 
     Like the upper photoelectric layer  430 , the high-concentration impurity regions  424  and  426  of the lower photoelectric layer  420  may be either large or small, and the large high-concentration impurity regions  424  and the small high-concentration impurity regions  426  may be alternately arranged. However, the size difference between the large high-concentration impurity region  424  and the small high-concentration impurity regions  426  may be insignificant compared with that in the upper photoelectric layer  430 . 
     The impurities in the photoelectric layers  420  and  430  may be introduced by ion implantation and/or a diffusion process. 
       FIG. 6(   b ) is a schematic illustration of a solar cell  400   b  according to example embodiments. The solar cell  400   b  illustrated in  FIG. 6(   b ) is like the solar cell  400   a  in  FIG. 6(   a ), except the solar cell  400   b  further includes wavelength conversion members  485  and  495  in the low-concentration impurity regions  432 ′ and  422 ′ of the upper photoelectric layer  430 ′ and the lower photoelectric layer  420 ′ respectively. The materials for the wavelength conversion members  485  and  495  may be the same as the materials of the wavelength conversion members  380  and  390  shown in  FIGS. 5(   a ) and  5 ( b ). One of the wavelength conversion members  485  and  495  may be omitted. 
       FIG. 6(   c ) a schematic illustration of a solar cell  400   c  according to example embodiments. The solar cell  400   c  illustrated in  FIG. 6(   c ) is like the solar cell  400   a  in  FIG. 6(   a ), except the solar cell  400   c  further includes passivation layers  490  and  480  between the base substrate  410  and the upper  430  and lower  420  photoelectric layers. The passivation layers  490  and  480  may contain the same materials as the passivation layers  290  and  280  discussed above with reference to  FIG. 4 . One of the passivation layers  485  and  495  may be omitted. 
       FIG. 6(   d ) a schematic illustration of a solar cell  400   d  according to example embodiments. The solar cell  400   d  illustrated in  FIG. 6(   d ) is like the solar cell  400   a  in  FIG. 6(   a ), except the solar cell  400   d  further includes passivation layers  490  and  480  between the base substrate  410  and the upper  430  and lower  420  photoelectric layers and the solar cell  400   d  further includes wavelength conversion members  485  and  495  in the low-concentration impurity regions  432 ′ and  422 ′ of the upper photoelectric layer  430 ′ and the lower photoelectric layer  420 ′ respectively. 
       FIG. 6(   e ) a schematic illustration of a solar cell  400   e  according to example embodiments. The solar cell  400   e  illustrated in  FIG. 6(   e ) is like the solar cell  400   c  in  FIG. 6(   c ), except the solar cell  400   e  further includes wavelength conversion members  465  and  475  in the base substrate  410 ′. The wavelength conversion members  465  and  475  may contain the same materials as the wavelength conversion members  485  and  495  described above. One of the wavelength conversion members  465  and  475  may be omitted. One of the passivation layers  490  and  480  may be omitted. 
       FIG. 6(   f ) is a schematic illustration of a solar cell  400   f  according to example embodiments. The solar cell  400   f  is like the solar cell  400   e , except the passivation members  490  and  480  are omitted. 
       FIG. 6(   g ) is a schematic illustration of a solar  400   g  according to example embodiments. The solar cell  400   g  is like the solar cell  400   a  shown in  FIG. 6(   a ), except the solar cell  400   g  further includes wavelength conversion members  485  in the upper photoelectric layer  430 ′ and wavelength conversion members  475  in the base substrate  410 ″. 
       FIG. 6(   h ) is a schematic illustration of a solar  400   h  according to example embodiments. The solar cell  400   h  is like the solar cell  400   a  shown in  FIG. 6(   a ), except the solar cell  400   h  further includes wavelength conversion members  495  in the lower photoelectric layer  420 ′ and wavelength conversion members  465  in the base substrate  410 ′″. 
     The solar cells  400   g  and  400   h  illustrated in  FIGS. 6(   g ) and  6 ( h ) may further include at least one of the passivation layers  490  and  480  between the base substrate  410 ″ or  410 ′″ and the upper photoelectric layer  430  or  430 ′ and/or lower photoelectric layer  420  or  420 ′, as described above. 
     Although  FIGS. 1 to 4 ,  5 ( a ),  5 ( b ), and  6 ( a ) to  6 ( h ) illustrate schematic sectional views of solar cells according to example embodiments, example embodiments are not limited thereto. One having ordinary skill in the art would appreciate that one or more of the foregoing solar cells according to example embodiments may be electrically connected in series, parallel, and series-parallel arrangements in order to form a solar cell module configured to generate desired current, voltage, and/or power characteristics. 
     According to example embodiments, since the photoelectric layers having different energy bandgaps are electrically separated, the currents generated from the photoelectric layers may be collected to be used in a whole, thereby increasing the efficiency of power generation. In addition, the photoelectric layers are formed in forms of thin films under and on the transparent supporting base substrate, the manufacturing process may be simple and the manufacturing cost may be reduced. 
     While some example embodiments have been particularly shown and described, it will be understood by one of ordinary skill in the art that variations in form and detail may be made therein without departing from the spirit and scope of the claims.