Patent Publication Number: US-2012042948-A1

Title: Thin-film solar cell and manufacture method thereof

Description:
This application claims priority to Taiwan Patent Applications No. 099107834 and No. 099107836 filed on Mar. 17, 2010, which are hereby incorporated by reference in their entirety. 
     CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a solar cell and a manufacturing method thereof, and more particularly, to a thin-film solar cell with improved photoelectric conversion efficiency and a manufacturing method thereof. 
     2. Descriptions of the Related Art 
     Due to shortage of fossil energy resources and enhanced awareness of environmental protection, great efforts have been made continuously in recent years on development and research of technologies related to alternative energy resources and renewable energy resources. This is intended to reduce the level of dependence on fossil energy resources and influence of consumption of fossil energy resources on the environment. Among various technologies related to alternative energy resources and renewable energy resources, the solar cell has received the most attention. This is mainly because that the solar cell can convert the solar energy directly into the electric energy without emission of hazardous materials that may pollute the environment such as carbon dioxide or nitrides during electric power generation. 
     Generally, a conventional thin-film solar cell is typically formed by sequentially stacking an electrode layer, a photoelectric conversion layer and an electrode layer throughout a substrate. When light rays from the outside impinge on the thin-film solar cell, the photoelectric conversion layer irradiated by the light rays is adapted to generate free electron-hole pairs. Under action of a built-in electric field formed by the PN junction, the electrons and the holes migrate towards the two electrode layers respectively to result in an electric energy storage status. Then, if a load circuit or an electronic device is externally connected across the solar cell, the electric energy can be supplied to drive the load circuit or the electronic device. 
     However, thin-film solar cells currently available have photoelectric conversion efficiency as low as about 6%˜10% on average, and currently there still exists a bottleneck in improving the photoelectric conversion efficiency of the thin-film solar cells. Accordingly, efforts still have to be made in the art to provide a solution that can improve the photoelectric conversion efficiency of the thin-film solar cells. 
     SUMMARY OF THE INVENTION 
     The present invention provides a thin-film solar cell, which can enhance the utilization factor of light beams to improve the photoelectric conversion efficiency of the thin-film solar cell. 
     The thin-film solar cell of the present invention comprises a transparent substrate, a first transparent conductive layer, a photovoltaic layer, a second transparent conductive layer and a light reflecting structure. The transparent substrate has a light incident surface and a light exiting surface opposite to the light incident surface. The first transparent conductive layer is disposed on the light exiting surface of the transparent substrate. The photovoltaic layer is disposed on the first transparent conductive layer. The second transparent conductive layer is disposed on the photovoltaic layer. The light reflecting structure is disposed on the second transparent conductive layer, wherein a light beam enters the thin-film solar cell via the light incident surface, passes sequentially through the transparent substrate, the first transparent conductive layer, the photovoltaic layer and the second transparent conductive layer and then into the light reflecting structure, and the light reflecting structure reflects the light beam. 
     In an embodiment of the present invention, the light reflecting structure comprises a patterned structure. The patterned structure has a first sub-pattern structure and a second sub-pattern structure. The first sub-pattern structure is disposed on the second transparent conductive layer, the second sub-pattern structure is disposed on the first sub-pattern structure, and the second sub-pattern structure at least partially overlaps the first sub-pattern structure. 
     In an embodiment of the present invention, the patterned structure may be of a straight stripe form, a stripe form, a transverse stripe form, a check form, a rhombus form, a honeycomb form or a mosaic form. 
     In an embodiment of the present invention, a surface where the first sub-pattern structure makes contact with the second transparent conductive layer is a texture structure. 
     In an embodiment of the present invention, at least a surface where the second sub-pattern structure makes contact with the first sub-pattern structure is a texture structure. 
     In an embodiment of the present invention, the light reflecting structure is a light reflecting structure layer, and the light reflecting structure layer is integrally formed. 
     In an embodiment of the present invention, the light reflecting structure layer entirely or partially covers the second transparent conductive layer. 
     In an embodiment of the present invention, a surface where the light reflecting structure layer makes contact with the second transparent conductive layer is a texture structure. 
     In an embodiment of the present invention, the light reflecting structure is made of one or more materials selected from a group consisting of a white paint, a metal, a metal oxide and an organic material. 
     In an embodiment of the present invention, the metal is selected from a group consisting of aluminum (Al), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), indium (In), tin (Sn), antimony (Sb), lanthanum (La), gadolinium (Gd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), thallium (Tl), lead (Pb) and alloys thereof. 
     In an embodiment of the present invention, the metal oxide comprises an indium oxide, a tin oxide, a silicon oxide, a magnesium fluoride, a tantalum oxide, a titanium oxide, a magnesium oxide, a zirconium oxide, a silicon nitride, an aluminum oxide, a hafnium oxide, a indium tin oxide (ITO), a cadmium stannate (Cd2SnO4), a cadmium stannate doped with copper, a stannic oxide or a stannic oxide doped with fluorine. 
     In an embodiment of the present invention, the organic material comprises a dye or a pigment. 
     In an embodiment of the present invention, a part of the light beam comprises a red light, a near infrared (IR) light or a far IR light. 
     In an embodiment of the present invention, the photovoltaic layer is a group IV element thin film, a group III-V compound semiconductor thin film, a group II-VI compound semiconductor thin film, an organic compound semiconductor thin film or a combination thereof. 
     In an embodiment of the present invention, the group IV element thin film comprises at least one of an a-Si thin film, a μc-Si thin film, an a-SiGe thin film, a μc-SiGe thin film, an a-SiC thin film, a μc-SiC thin film, a tandem group IV element thin film or a triple group IV element thin film. 
     In an embodiment of the present invention, the group III-V compound semiconductor thin film comprises gallium arsenide (GaAs), indium gallium phosphide (InGaP) or a combination thereof. 
     In an embodiment of the present invention, the group II-VI compound semiconductor thin film comprises copper indium selenium (CIS), copper indium gallium selenium (CIGS), cadmium telluride (CdTe) or a combination thereof. 
     In an embodiment of the present invention, the organic compound semiconductor thin films comprise a mixture of poly(3-hexylthiophene) (P3HT) and carbon nanospheres (PCBM). 
     In an embodiment of the present invention, the transparent substrate is a glass substrate. 
     According to the above descriptions, the thin-film solar cell of the present invention has a light reflecting structure disposed on the second transparent conductive layer to increase the opportunity for the light beam to be reflected in the thin-film solar cell. This can prolong the light path of the light beam in the photovoltaic layer so that the light beam will be more likely absorbed by the photovoltaic layer to generate more electron-hole pairs. In other words, the thin-film solar cell employing the light reflecting structure can effectively enhance the utilization factor of the light beam to improve the photoelectric conversion efficiency thereof. 
     The present invention also provides a method for manufacturing a thin-film solar cell, which can form a light reflecting structure having a texture structure on a layer. This can enhance the utilization factor of the light beam in the thin-film solar cell, thus resulting in improved photoelectric conversion efficiency of the thin-film solar cell. 
     The method for manufacturing a thin-film solar cell of the present invention comprises the following steps of: providing a transparent substrate; forming a first transparent conductive layer on the transparent substrate; forming a photovoltaic layer on the first transparent conductive layer; forming a second transparent conductive layer on the photovoltaic layer; and forming a light reflecting structure having a texture structure on the second transparent conductive layer. 
     In an embodiment of the present invention, the light reflecting structure is formed through an impression process. 
     In an embodiment of the present invention, the impression process comprises: forming a reflective material layer on the second transparent conductive layer entirely; and impressing a mold with a texture pattern onto the reflective material layer to form the light reflecting structure having the texture structure. 
     In an embodiment of the present invention, the impression process comprises: forming a transparent material layer on the second transparent conductive layer entirely; impressing a mold with a texture pattern onto the transparent material layer to form the texture structure on the surface of the transparent material layer; and forming a reflective material layer on the transparent material layer. 
     In an embodiment of the present invention, the reflective material layer is conformal to the transparent material layer. 
     In an embodiment of the present invention, the impression process comprises: impressing a first sub-pattern structure on the second transparent conductive layer; and impressing a second sub-pattern structure on the first sub-pattern structure, wherein the second sub-pattern structure at least partially overlaps the first sub-pattern structure to form the light reflecting structure. 
     In an embodiment of the present invention, the light reflecting structure may be of a straight stripe form, a stripe form, a transverse stripe form, a check form, a rhombus form, a honeycomb form or a mosaic form. 
     In an embodiment of the present invention, the light reflecting structure is formed through a mesh process. 
     In an embodiment of the present invention, the mesh process comprises: disposing a mold having a mesh pattern on the second transparent conductive layer, wherein the mesh pattern has a plurality of openings exposing the second transparent conductive layer; forming a reflective material layer on the mold, wherein portions of the reflective material layer is filled into the openings to connect to the second transparent conductive layer; and removing the mold to form the light reflecting structure having the texture structure. 
     In an embodiment of the present invention, the mesh process comprises: forming a transparent material layer on the second transparent conductive layer entirely; impressing a mold with a mesh pattern onto the transparent material layer to form the mesh pattern on a surface of the transparent material layer; removing the mold; and forming a reflective material layer on the transparent material layer. 
     In an embodiment of the present invention, the mesh process comprises: disposing a first mold with a first mesh pattern on the second transparent conductive layer, wherein the first mesh pattern has a plurality of first openings exposing the second transparent conductive layer; forming a first sub-pattern structure on the first mold, wherein the first sub-pattern structure connects with portions of the second transparent conductive layer; disposing a second mold with a second mesh pattern on the first sub-pattern structure, wherein the second mesh pattern has a plurality of second openings exposing at least portions of the first openings; and forming a second sub-pattern structure on the first sub-pattern structure, wherein the second sub-pattern structure at least partially overlaps the first sub-pattern structure to form the light reflecting structure. 
     In an embodiment of the present invention, the organic material comprises a dye or a pigment. 
     In an embodiment of the present invention, the transparent substrate has a light incident surface, wherein a light beam enters the thin-film solar cell via the light incident surface, passes sequentially through the transparent substrate, the first transparent conductive layer, the photovoltaic layer and the second transparent conductive layer and then into the light reflecting structure. The light reflecting structure reflects the light beam. 
     In an embodiment of the present invention, the method for manufacturing a thin-film solar cell further comprises covering an adhesive layer on the light reflective structure to package a counter transparent substrate and the transparent substrate together. 
     According to the above descriptions, the method for manufacturing a thin-film solar cell of the present invention forms a light reflecting structure having a texture structure on the second transparent conductive layer to increase the opportunity for the light beam to be reflected in the thin-film solar cell. This can prolong the light path of the light beam in the photovoltaic layer so that the light beam will be more likely absorbed by the photovoltaic layer to generate more electron-hole pairs. In other words, the method for manufacturing a thin-film solar cell of the present invention can effectively enhance the utilization factor of the light beam in the resulting thin-film solar cell, thus improving the photoelectric conversion efficiency of the thin-film solar cell. 
     The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a thin-film solar cell according to an embodiment of the present invention; 
         FIGS. 2A to 2D  are schematic top views of a light reflecting structure according to different embodiments of the present invention; 
         FIG. 3  is a schematic cross-sectional view of a thin-film solar cell according to another embodiment of the present invention; 
         FIG. 4  is a schematic cross-sectional view of a thin-film solar cell according to another embodiment of the present invention; 
         FIG. 5  is a schematic cross-sectional view of a thin-film solar cell according to another embodiment of the present invention; 
         FIG. 6  is a schematic cross-sectional view of a thin-film solar cell according to another embodiment of the present invention; 
         FIG. 7  is a schematic cross-sectional view of a thin-film solar cell according to another embodiment of the present invention; 
         FIGS. 8A to 8D  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to an embodiment of the present invention; 
         FIGS. 9A to 9D  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention; 
         FIGS. 10A to 10C  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention; 
         FIGS. 11A and 11B  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention; 
         FIGS. 12A to 12D  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention; 
         FIGS. 13A to 13D  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention; and 
         FIGS. 14A to 14E  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a schematic cross-sectional view of a thin-film solar cell according to an embodiment of the present invention. Referring to  FIG. 1 , in this embodiment, the thin-film solar cell  100   a  comprises a transparent substrate  110 , a first transparent conductive layer  120 , a photovoltaic layer  130 , a second transparent conductive layer  140  and a light reflecting structure  150 . 
     The transparent substrate  110  has a light incident surface  110   a  and a light exiting surface  110   b  opposite to the light incident surface  110   a . The transparent substrate  110  is, for example, a glass substrate. The first transparent conductive layer  120  is disposed on the light exiting surface  110   b  of the transparent substrate  110 . The photovoltaic layer  130  is disposed on the first transparent conductive layer  120 . The second transparent conductive layer  140  is disposed on the photovoltaic layer  130 . The light reflecting structure  150  is disposed on the second transparent conductive layer  140 . A light beam L 1  enters the thin-film solar cell  100   a  via the light incident surface  110   a , passes sequentially through the transparent substrate  110 , the first transparent conductive layer  120 , the photovoltaic layer  130  and the second transparent conductive layer  140  and then into the light reflecting structure  150 , and is reflected by the light reflecting structure  150 . 
     Generally, the first transparent conductive layer  120  and the second transparent conductive layer  140  may both be made of a transparent conductive material such as indium tin oxide (ITO), indium zinc oxide (IZO), indium tin zinc oxide (ITZO), zinc oxide, aluminum tin oxide (ATO), aluminum zinc oxide (AZO), cadmium indium oxide (CIO), cadmium zinc oxide (CZO), gallium zinc oxide (GZO) and fluorine-doped tin oxide (FTO), or a combination thereof. 
     The photovoltaic layer  130  may be a group IV element thin film, a group III-V compound semiconductor thin film, a group II-VI compound semiconductor thin film, an organic compound semiconductor thin film or a combination thereof. In detail, the group IV element thin film comprises, for example, at least one of an a-Si thin film, a μc-Si thin film, an a-SiGe thin film, a μc-SiGe thin film, an a-SiC thin film, a μc-SiC thin film, a tandem group IV element thin film (e.g., a stacked silicon thin film) or a triple group IV element thin film. The group III-V compound semiconductor thin film comprises, for example, gallium arsenide (GaAs), indium gallium phosphide (InGaP) or a combination thereof. The group II-VI compound semiconductor thin film comprises, for example, copper indium selenium (CIS), copper indium gallium selenium (CIGS), cadmium telluride (CdTe) or a combination thereof. The organic compound semiconductor thin films comprise, for example, a mixture of poly(3-hexylthiophene) (P3HT) and carbon nanospheres (PCBM). 
     In other words, the thin-film solar cell  100   a  may adopt a layered structure of an amorphous silicon thin-film solar cell, a microcrystalline silicon thin-film solar cell, a tandem thin-film solar cell, a triple thin-film solar cell, a CIS thin-film solar cell, a CIGS thin-film solar cell, a CdTe thin-film solar cell or an organic thin-film solar cell. That is, depending on the user&#39;s design and requirements on the photovoltaic layer  130 , the thin-film solar cell  100   a  of this embodiment may also be of other possible layered structures; and what described above is only for illustration purpose but is not to limit the present invention. 
     As shown in  FIG. 1 , the light reflecting structure  150  of this embodiment is, for example, a patterned structure  150   a . The patterned structure  150   a  comprises a first sub-pattern structure  152  and a second sub-pattern structure  154 . The first sub-pattern structure  152  is disposed on the second transparent conductive layer  140 , and the second sub-pattern structure  154  is disposed on the first sub-pattern structure  152  and at least partially overlaps the first sub-pattern structure  152 . That is, the second sub-pattern structure  154  only partially overlaps the first sub-pattern structure  152 ; in other words, portions of the second sub-pattern structure  154  is disposed on the second transparent conductive layer  140 . 
     Specifically, after entering the thin-film solar cell  100   a  via the light incident surface  110   a  of the transparent substrate  110 , the light beam L 1  sequentially passes through the transparent substrate  110 , the first transparent conductive layer  120  and the photovoltaic layer  130 . A part of the light beam L 1  that is unabsorbed by the photovoltaic layer  130  is then transmitted through the second transparent conductive layer  140  to the patterned structure  150   a . Then, the first sub-pattern structure  152  and the second sub-pattern structure  154  of the patterned structure  150   a  can reflect a part L 2  of the light beam L 1  to the photovoltaic layer  130 . In this embodiment, the light beam L 2  is, for example, a red light, a near infrared (IR) light or a far IR light. 
     In other words, by using the stack structure formed by the first sub-pattern structure  152  and the second sub-pattern structure  154  to affect the propagation direction of the light beam L 1 , the light beam L 1  is reflected at the interface between the patterned structure  150   a  and the second transparent conductive layer  140 . Thus, the patterned structure  150   a  can increase the opportunity for the light beam L 1  to be reflected in the thin-film solar cell  100   a . This can prolong the light path of the light beam L 1  in the photovoltaic layer  130  and, consequently, increase the opportunity for the light beam to be absorbed by the photovoltaic layer  130 . As a result, the thin-film solar cell  100   a  can effectively utilize and absorb the light beam L 1  and convert it into electric energy, thus resulting in higher photoelectric conversion efficiency. 
     In this embodiment, by modifying the form of the patterned structure  150   a  or forming the light reflecting structure  150  of different materials, an objective of reflecting a part L 2  of the light beam L 1  can be achieved. Specifically, the patterned structure  150   a  of this embodiment is of, for example, a check form formed by orthogonal intersection of the first sub-pattern structure  152  and the second sub-pattern structure  154  as shown in  FIG. 2A ; a rhombus form formed by intersection of the first sub-pattern structure  152  and the second sub-pattern structure  154  at an angle as shown in  FIG. 2B ; a straight stripe form (shown in  FIG. 2C ), a regular or irregular stripe form (not shown) or a transverse stripe form (not shown) formed by parallel arrangement and partial overlapping between the first sub-pattern structure  152  and the second sub-pattern structure  154 ; or a mosaic form (shown in  FIG. 2D ) or a honeycomb form (not shown) formed through regular or irregular arrangement of the first sub-pattern structure  152  and the second sub-pattern structure  154 . In other words, the arrangement and structures of the first sub-pattern structure  152  and the second sub-pattern structure  154  can be varied depending on the user&#39;s requirements; and what described above is only for illustration purpose but is not to limit the present invention. 
     Additionally, the light reflecting structure  150  may be made of one or more materials selected from a group consisting of a white paint, a metal, a metal oxide and an organic material. The metal is selected from a group consisting of aluminum (Al), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), indium (In), tin (Sn), antimony (Sb), lanthanum (La), gadolinium (Gd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), thallium (Tl), lead (Pb) and alloys thereof. The metal oxide may be selected from an indium oxide, a tin oxide, a silicon oxide, a magnesium fluoride, a tantalum oxide, a titanium oxide, a magnesium oxide, a zirconium oxide, a silicon nitride, an aluminum oxide, a hafnium oxide, a indium tin oxide (ITO), a cadmium stannate (Cd2SnO4), a cadmium stannate doped with copper, a stannic oxide or a stannic oxide doped with fluorine. The organic material may be a dye or a pigment. 
     Additionally, in an embodiment not shown, the patterned structure may also be a poly-layer formed by a plurality of first polymer materials and a plurality of second polymer materials alternately arranged. The first polymer materials are, for example, hydroxyl acetoxylated polyethylene terephthalate (PET) or a copolymer of hydroxyl acetoxylated polyethylene terephthalate, and the second polymer materials are, for example, polyethylene naphthalate (PEN) or a copolymer of polyethylene naphthalate. However, the materials described above are only provided as examples, and materials that can have the light reflecting structure  150  reflect the light beam all fall within the scope of the present invention. 
     Hereinbelow, designs of the thin-film solar cells  100   b ˜ 100   f  will be described with reference to several embodiments. It shall be appreciated herein that, some of the reference numerals and contents of the above embodiments apply also to the following embodiments, wherein identical reference numerals are used to denote the same or similar elements, and descriptions of identical technical contents will be omitted. For descriptions of the omitted portions, reference may be made to the aforesaid embodiments. 
       FIG. 3  is a schematic cross-sectional view of a thin-film solar cell according to another embodiment of the present invention. Referring to  FIG. 1  and  FIG. 3  together, the thin-film solar cell  100   b  of this embodiment is similar to the thin-film solar cell  100   a  of  FIG. 1  except that: the light reflecting structure  150  of this embodiment is a patterned structure  150   b , and a surface where the first sub-pattern structure  152   a  of the patterned structure  150   b  makes contact with the second transparent conductive layer  140  is, for example, a texture structure  153   a . To be more specific, the patterned structure  150   b  of this embodiment covers the second transparent conductive layer  140  entirely, and the surface where the first sub-pattern structure  152  makes contact with the second transparent conductive layer  140  is the texture structure  153   a  which is, for example, a surface microstructure formed on the surface of the first sub-pattern structure  152   a . Of course, in other embodiments not shown, the texture structure  153   a  may also be a surface microstructure formed on the surface of the second transparent conductive layer  140 . 
     Because the surface where the patterned structure  150   b  makes contact with the second transparent conductive layer  140  is a texture structure  153   a , it becomes easier for the light beam L 1  propagating to the texture structure  153   a  to be reflected by the texture structure  153   a  and for the reflected light beam L 2  to be scattered. This can prolong the light path of the light beam L 2  in the photovoltaic layer  130  and, consequently, increase the opportunity for the light beam L 2  to be absorbed by the photovoltaic layer  130 , thus improving the overall photoelectric conversion efficiency. Furthermore, the part L 2  of the light beam L 1  can be reflected directly by the patterned structure  150   b  to the photovoltaic layer  130 . In other words, the first sub-pattern structure  152   a  and the second sub-pattern structure  154  of the patterned structure  150   b  can affect the propagation direction of the light beam L 1  in such a way that the light beam L 1  is reflected and scattered by the surface where the first sub-pattern structure  152   a  makes contact with the second transparent conductive layer  140  or in such a way that the light beam L 1  is reflected by the second patterned structure  154 . In this way, the opportunity for the light beam L 1  to be reflected in the thin-film solar cell  100   b  can be increased to prolong the light path of the light beam L 1  in the photovoltaic layer  130  so that the light beam L 1  will be more likely absorbed by the photovoltaic layer  130  to generate more electron-hole pairs. In other words, the thin-film solar cell  100   b  can effectively enhance the utilization factor of the light beam L 1  to improve the photoelectric conversion efficiency. 
       FIG. 4  is a schematic cross-sectional view of a thin-film solar cell according to another embodiment of the present invention. Referring to  FIG. 3  and  FIG. 4  together, the thin-film solar cell  100   c  of this embodiment is similar to the thin-film solar cell  100   b  of  FIG. 3  except that: in this embodiment, a surface where the second sub-pattern structure  154   b  makes contact with the first sub-pattern structure  152  is a texture structure  153   b  which is, for example, a surface microstructure formed on the surface of the second sub-pattern structure  154   a . Of course, in other embodiments not shown, the texture structure  153   b  may also be a surface microstructure formed on the surface of the first sub-pattern structure  152 . 
       FIG. 5  is a schematic cross-sectional view of a thin-film solar cell according to another embodiment of the present invention. Referring to  FIG. 3  and  FIG. 5  together, the thin-film solar cell  100   d  of this embodiment is similar to the thin-film solar cell  100   b  of  FIG. 3  except that: in this embodiment, a surface where the first sub-pattern structure  152   b  makes contact with the second transparent conductive layer  140  is, for example, a texture structure  153   a , and a surface where the second sub-pattern structure  154   b  makes contact with the first sub-pattern structure  152   b  is a texture structure  153   b . The texture structure  153   a  is, for example, a surface microstructure formed on the surface of the first sub-pattern structure  152   b , and the texture structure  153   b  is, for example, a surface microstructure formed on the surface of the second sub-pattern structure  154   b . Of course, in other embodiments not shown, the texture structure  153   a  may also be a surface microstructure formed on the surface of the second transparent conductive layer  140 , and the texture structure  153   b  may also be a surface microstructure formed on the surface of the first sub-pattern structure  152   b.    
     It shall be appreciated herein that, the present invention has no limitation on configurations of the patterned structures  150   a ˜ 150   d . Although the patterned structures  150   a ˜ 150   d  set forth herein are described to have the first sub-pattern structures  152 ,  152   a ,  152   b  and the second sub-pattern structures  154 ,  154   a ,  154   b  (i.e., each of the patterned structures  150   a ˜ 150   d  consists of two layers of patterned structures), other designs capable of achieving the equivalent effect of reflecting a light beam (e.g., the patterned structure is a layer of continuous structure, a layer of discontinuous structure, a plurality of layers of continuous structures or a plurality of discontinuous structures) can also be adopted in the present invention without departing from the scope of the present invention. 
       FIG. 6  is a schematic cross-sectional view of a thin-film solar cell according to another embodiment of the present invention. Referring to  FIG. 1  and  FIG. 6  together, the thin-film solar cell  100   e  of this embodiment is similar to the thin-film solar cell  100   a  of  FIG. 1  except that, the light reflecting structure  150  of this embodiment is a light reflecting structure layer  150   e  and the light reflecting structure layer  150   e  is integrally formed. The light reflecting structure layer  150   e  covers the second transparent conductive layer  140  entirely to increase the opportunity for the light beam L 1  to be reflected in the thin-film solar cell  100   e . This can prolong the light path of the light beam L 1  in the photovoltaic layer  130  so that the light beam L 1  will be more likely absorbed by the photovoltaic layer  130  to generate more electron-hole pairs. In other words, the thin-film solar cell  100   e  can effectively enhance the utilization factor of the light beam L 1  to improve the photoelectric conversion efficiency thereof. 
     It is worth noting that, the present invention has no limitation on configurations of the light reflecting structure layer  150   e . Although the light reflecting structure layer  150   e  set forth herein is described to entirely cover the second transparent conductive layer  140 , other designs capable of achieving the equivalent effect of reflecting a light beam (e.g., the light reflecting structure layer  150   e  only partially covers the second transparent conductive layer  140 ) can also be adopted in the present invention without departing from the scope of the present invention. 
       FIG. 7  is a schematic cross-sectional view of a thin-film solar cell according to another embodiment of the present invention. Referring to  FIG. 6  and  FIG. 7  together, the thin-film solar cell  100   f  of this embodiment is similar to the thin-film solar cell  100   e  of  FIG. 6  except that: in this embodiment, a surface where the light reflecting structure layer  150   f  makes contact with the second transparent conductive layer  140  is a texture structure  153   c  which is, for example, a surface microstructure formed on the surface of the light reflecting structure layer  150   f . Of course, in other embodiments not shown, the texture structure  153   c  may also be a surface microstructure formed on the surface of the second transparent conductive layer  140 . 
     According to the above descriptions, the present invention has a light reflecting structure disposed on the second transparent conductive layer to increase the opportunity for the light beam to be reflected in the thin-film solar cell. This can prolong the light path of the light beam in the photovoltaic layer so that the light beam will be more likely absorbed by the photovoltaic layer to generate more electron-hole pairs. In other words, the thin-film solar cell employing the light reflecting structure can effectively enhance the utilization factor of the light beam to improve the photoelectric conversion efficiency thereof. Furthermore, through design of the texture structure, the light beam can be reflected and scattered to the photovoltaic layer to prolong the light path of the light beam in the photovoltaic layer; this also increases the opportunity for the light beam to be absorbed by the photovoltaic layer to improve the overall photoelectric conversion efficiency. 
     Hereinbelow, methods for manufacturing a thin-film solar cell will be described with reference to several different embodiments. It shall be appreciated herein that, the following embodiments are intended to disclose methods for manufacturing the aforesaid thin-film solar cells, so some of the reference numerals and contents of the above embodiments will also apply to the following embodiments; in terms of this, identical reference numerals will be used to denote the same or similar elements, and descriptions of identical technical contents (including descriptions of materials of elements, shapes of the elements and how the elements are connected) will be omitted. For descriptions of the omitted portions, reference may be made to the aforesaid embodiments of the thin-film solar cell. 
       FIGS. 8A to 8D  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to an embodiment of the present invention, in which  FIG. 8C  is a schematic cross-sectional view of forming a light reflecting structure having a texture structure according to another embodiment. Referring to  FIG. 8A , firstly, a transparent substrate  110  is provided. The transparent substrate  110 , which is a glass substrate for example, has a light incident surface  110   a . Then, a first transparent conductive layer  120 , a photovoltaic layer  130  and a second transparent conductive layer  140  are sequentially formed on a light exiting surface of the transparent substrate  110  opposite to the light incident surface  110   a.    
     In this embodiment, the first transparent conductive layer  120  is formed on the transparent substrate  110 . The first transparent conductive layer  120  may be formed through a sputtering process, a metal organic chemical vapor deposition (MOCVD) process or an evaporation process. 
     Still referring to  FIG. 8A , in this embodiment, the photovoltaic layer  130  is formed on the first transparent conductive layer  120 . The photovoltaic layer  130  is formed through, for example, a radio frequency plasma enhanced chemical vapor deposition (RF PECVD) process, a very high frequency plasma enhanced chemical vapor deposition (VHF PECVD) process or a microwave plasma enhanced chemical vapor deposition (MW PECVD) process. 
     After formation of the photovoltaic layer  130 , the second transparent conductive layer  140  is formed on the photovoltaic layer  130 , as shown in  FIG. 8A . In this embodiment, the way in which the second transparent conductive layer  140  is formed is the same as way in which the first transparent conductive layer  120  is formed. Next, referring also to  FIG. 8A , a reflective material layer  162  is formed on the second transparent conductive layer  140  entirely; i.e., the reflective material layer  162  covers the second transparent conductive layer  140  completely. Thereafter, a mold M 1  having a texture pattern P is provided on the reflective material layer  162 . 
     Afterwards, the mold M 1  having the texture pattern P is mechanically impressed onto the reflective material layer  162 , as shown in  FIG. 8B . Then, the reflective material layer  162   a  is cured to form a light reflecting structure  150  having the texture structure P. That is, after the impressing with the mold M and the curing, the reflective material layer  162   a  having the texture structure P just serves as the light reflecting structure  150 . Of course, in other embodiments, as shown in  FIG. 8C , another kind of light reflecting structure  150   g  exposing portions of the second transparent conductive layer  140  may also be formed by impressing a mold M 1 ′ having a texture pattern P′ onto the reflective material layer  162 . That is, after the impressing with the mold M 1 ′ and the curing, the reflective material layer  162   b  having the texture structure P′ and exposing portions of the second transparent conductive layer  140  just serves as the light reflecting structure  150 . As can be known from above, in this embodiment, the light reflecting structures  150 ,  150   g  may be formed through the impression process, wherein the force applied in the mechanical impression process may depend on the configurations of the light reflecting structures  150 ,  150   g.    
     Upon completion of the step shown in  FIG. 8B , the mold M 1  is removed and an adhesive layer  170  is applied on the light reflecting structure  150  to package a counter transparent substrate  180  and the transparent substrate  110  together, as shown in  FIG. 8D . In this embodiment, the adhesive layer  170  is made of, for example, an adhesive such as ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), poly olefin or polyurethane (PU). The counter transparent substrate  180  is, for example, a glass substrate. Here, the way of using the adhesive layer  170  to package the transparent substrate  110  and the counter transparent substrate  180  is well known to those of ordinary skill in the art, so no further description will be made thereon. Thus, fabrication of the thin-film solar cell  100   g  is substantially completed. 
     As shown in  FIG. 8D , because the thin-film solar cell  100   g  of this embodiment comprises the light reflecting structure  150 , the light beam L 1  entering the thin-film solar cell  100   g  via the light incident surface  110   a  of the transparent substrate  110  sequentially passes through the transparent substrate  110 , the first transparent conductive layer  120  and the photovoltaic layer  130 , and a part of the light beam L 1  unabsorbed by the photovoltaic layer  130  further passes through the second transparent conductive layer  140  to the reflective material layer  162   a . Then, it becomes easier for the light beam L 1  to be reflected by the texture structure P of the reflective material layer  162   a  and for the reflected light beam L 2  to be scattered. This can prolong the light path of the light beam L 2  in the photovoltaic layer  130  and, consequently, increase the opportunity for the light beam L 2  to be absorbed by the photovoltaic layer  130 , thus resulting in improved photoelectric conversion efficiency. Here, the texture structure P reflects and scatters the reflected light beam L 2 , and the light beam L 2  is, for example, a red light, a near IR light or a far IR light. 
     In other words, by means of the reflective material layer  162   a  having the texture structure P that can affect the propagation direction of the light beam L 1 , the light beam L 1  is reflected and scattered at the interface between the reflective material layer  162   a  and the second transparent conductive layer  140 . Thus, the reflective material layer  162   a  can increase the opportunity for the light beam L 1  to be reflected in the thin-film solar cell  100   g . This can prolong the light path of the light beam L 1  in the photovoltaic layer  130  and, consequently, increase the opportunity for the light beam to be absorbed by the photovoltaic layer  130 . In other words, the thin-film solar cell  100   g  can effectively absorb the light beam L 1  and convert it into electric energy, thus resulting in higher photoelectric conversion efficiency. 
       FIGS. 9A to 9D  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention. The process of forming the thin-film solar cell  100   h  is similar to that of forming the thin-film solar cell  100   g , and differences therebetween will be described below. 
     Referring to  FIG. 9A , after the second transparent conductive layer  140  is formed on the photovoltaic layer  130 , a transparent material layer  164  is formed on the second transparent conductive layer  140  entirely. Next, as shown in  FIG. 9B , a mold M 1  having a texture pattern P is impressed onto the transparent material layer  164 , and then the transparent material layer  164   a  is cured to form the texture structure P on a surface of the transparent material layer  164   a . Then, as shown in  FIG. 9C , the mold M 1  is removed and a reflective material layer  166  is formed on the transparent material layer  164   a . The reflective material layer  166  is conformal to the transparent material layer  164   a . Here, the reflective material layer  166  and the transparent material layer  164   a  conformal to each other can be viewed as a light reflecting structure  150   h . Thereafter, as shown in  FIG. 9D , the adhesive layer  170  is applied onto the light reflecting structure  150   h  to package the counter transparent substrate  180  and the transparent substrate  110  together, thus completing the fabrication of the thin-film solar cell  100   h.    
     In this embodiment, the stack structure formed by the transparent material layer  164   a  and the conformal reflective material layer  166  thereon can be viewed as the light reflecting structure  150   h , so when the light beam L 1  propagates to the light reflecting structure  150   h , the texture structure P on the surface of the transparent material layer  164   a  can also affect the propagation direction of the light beam L 1  in such a way that the light beam L 1  is reflected and scattered at the interface between the transparent material layer  164   a  and the second transparent conductive layer  140 . Furthermore, a part of the light beam L 1  that is not reflected and scattered by the texture structure P will further pass through the transparent material layer  164   a  and be reflected by the reflective material layer  166  as a light beam L 3 , thus prolonging the light paths of the light beams L 2  and L 3  in the photovoltaic layer  130 . This can increase the opportunity for the light beams L 2  and L 3  to be absorbed by the photovoltaic layer  130  to improve overall photoelectric conversion efficiency. In other words, the thin-film solar cell  100   h  can effectively absorb the light beam L 1  and convert it into electric energy, thus resulting in higher photoelectric conversion efficiency. 
       FIGS. 10A to 10C  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention. The process of forming the thin-film solar cell  100   i  is similar to that of forming the thin-film solar cell  100   g , and differences therebetween will be described below. 
     Referring to  FIG. 10A , after the second transparent conductive layer  140  is formed on the photovoltaic layer  130 , a first sub-pattern structure  152  exposing portions of the second transparent conductive layer  140  is imprinted on the second transparent conductive layer  140 . Then, a second sub-pattern structure  154  is imprinted on the first sub-pattern structure  152 . The second sub-pattern structure  154  at least partially overlaps the first sub-pattern structure  152  to form a light reflecting structure  150   i , as shown in  FIG. 10B . Thereafter, as shown in  FIG. 10B , the adhesive layer  170  is applied onto the light reflecting structure  150   i  to package the counter transparent substrate  180  and the transparent substrate  110  together, thus completing the fabrication of the thin-film solar cell  100   i.    
     It is worth noting that, in this embodiment, the patterned structure  150   i  is, for example, of a check form formed by orthogonal intersection of the first sub-pattern structure  152  and the second sub-pattern structure  154  as shown in  FIG. 2A ; a rhombus form formed by intersection of the first sub-pattern structure  152  and the second sub-pattern structure  154  at an angle as shown in  FIG. 2B ; a straight stripe form (shown in  FIG. 2C ), a regular or irregular stripe form (not shown) or a transverse stripe form (not shown) formed by parallel arrangement and partial overlapping between the first sub-pattern structure  152  and the second sub-pattern structure  154 ; or a mosaic form (shown in  FIG. 2D ) or a honeycomb form (not shown) formed through regular or irregular arrangement of the first sub-pattern structure  152  and the second sub-pattern structure  154 . In other words, the arrangement and structures of the first sub-pattern structure  152  and the second sub-pattern structure  154  can be varied depending on the user&#39;s requirements; and what described above is only for illustration purpose but is not to limit the present invention. 
     In this embodiment, the stack structure formed by the first sub-pattern structure  152  and the second sub-pattern structure  154  can affect the propagation direction of the light beam L 1  in such a way that the light beam L 1  is reflected and scatted at the interface between the light reflecting structure  150   i  and the second transparent conductive layer  140  to form a light beam L 2 . This increases the opportunity for the light beam L 1  to be reflected in the thin-film solar cell  100   i  and, consequently, prolongs the light path of the light beam L 2  in the photovoltaic layer  130  so that the light beam L 2  will be more likely be absorbed by the photovoltaic layer  130 . In this way, the thin-film solar cell  100   i  can effectively absorb the light beam L 1  and convert it into electric energy, thus resulting in higher photoelectric conversion efficiency. 
       FIGS. 11A and 11B  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention. The process of forming the thin-film solar cell  100   j  is similar to that of forming the thin-film solar cell  100   i , and differences therebetween will be described below. 
     Referring to  FIG. 11A , before impressing the first sub-pattern structure  152   a  on the second transparent conductive layer  140 , a texture structure P 1  is formed on the first sub-pattern structure  152   a . The texture structure P 1  is disposed on a surface where the first sub-pattern structure  152   a  makes contact with the second transparent conductive layer  140 . Here, the first sub-pattern structure  152   a  covers the second transparent conductive layer  140  entirely. Then as shown in  FIG. 11B , sequentially, the second sub-pattern structure  154   a  is imprinted on the first sub-pattern structure  152   a  and the adhesive layer  170  is applied onto the second sub-pattern structure  154   a  to package the counter transparent substrate  180  and the transparent substrate  110  together, thus completing the fabrication of the thin-film solar cell  100   j . Here, the second sub-pattern structure  154   a  covers the first sub-pattern structure  152   a  entirely, and the stack structure formed by the first sub-pattern structure  152   a  and the second sub-pattern structure  154   a  may be viewed as a light reflecting structure  150   j.    
     In this embodiment, the surface where the first sub-pattern structure  152   a  makes contact with the second transparent conductive layer  140  is a texture structure P 1  which is, for example, a surface microstructure formed on the surface of the first sub-pattern structure  152   a . Of course, in other embodiments not shown, the texture structure P 1  may also be a surface microstructure formed on the surface of the second transparent conductive layer  140 . Additionally, in an embodiment not shown, a surface where the second sub-pattern structure makes contact with the first sub-pattern structure may also be a texture structure, which may be a surface microstructure formed on either the first sub-pattern structure or the second sub-pattern structure, although the present invention is not limited thereto. 
     Because the surface where the first patterned structure  152   a  makes contact with the second transparent conductive layer  140  is the texture structure P 1 , it becomes easier for the light beam L 1  propagating to the texture structure P 1  to be reflected by the texture structure P 1  and for the reflected light beam L 2  to be scattered. This can prolong the light path of the light beam L 2  in the photovoltaic layer  130  and, consequently, increase the opportunity for the light beam L 2  to be absorbed by the photovoltaic layer  130 , thus improving the overall photoelectric conversion efficiency. Furthermore, the part L 2  of the light beam L 1  can be reflected directly by the light reflecting structure  150   j  to the photovoltaic layer  130 . In other words, the first sub-pattern structure  152   a  and the second sub-pattern structure  154   a  can affect the propagation direction of the light beam L 1  in such a way that the light beam L 1  is reflected and scattered by the surface where the first sub-pattern structure  152   a  makes contact with the second transparent conductive layer  140  or in such a way that the light beam L 1  is reflected by the second patterned structure  154 . In this way, the opportunity for the light beam L 1  to be reflected in the thin-film solar cell  100   j  can be increased to prolong the light path of the light beam L 1  in the photovoltaic layer  130  so that the light beam L 1  will be more likely absorbed by the photovoltaic layer  130  to generate more electron-hole pairs. Therefore, the thin-film solar cell  100   j  can effectively enhance the utilization factor of the light beam L 1  to improve the photoelectric conversion efficiency thereof. 
     It is worth noting that, in an embodiment not shown, the light reflecting structure may also be a poly-layer formed by a plurality of first polymer materials and a plurality of second polymer materials alternately arranged. The first polymer materials are, for example, hydroxyl acetoxylated polyethylene terephthalate (PET) or a copolymer of hydroxyl acetoxylated polyethylene terephthalate, and the second polymer materials are, for example, polyethylene naphthalate (PEN) or a copolymer of polyethylene naphthalate. However, the materials described above are only provided as examples, and materials that can have the light reflecting structure  150   j  reflect the light beam all fall within the scope of the present invention. 
       FIGS. 12A to 12D  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention. The process of forming the thin-film solar cell  100   k  is similar to that of forming the thin-film solar cell  100   g , and differences therebetween will be described below. 
     Referring to  FIG. 12A , after the second transparent conductive layer  140  is formed, a mold M 2  having a mesh pattern  200  is disposed on the second transparent conductive layer  140 . The mesh pattern  200  has a plurality of openings  202  exposing the second transparent conductive layer  140 . Next, as shown in  FIG. 12B , a reflective material layer  162   c  is formed on the mold M 2 , with portions of the reflective material layer  162   c  being filled into the openings  202  to connect with the second transparent conductive layer  140 . Next, as shown in  FIG. 12C , the mold M 2  is removed to form a light reflecting structure  150   k  having a texture structure P 2 . Afterwards, as shown in  FIG. 12D , the adhesive layer  170  is applied onto the light reflecting structure  150   k  to package the counter transparent substrate  180  and the transparent substrate  110  together, thus completing the fabrication of the thin-film solar cell  100   k.    
     In brief, this embodiment forms the light reflecting structure  150   k  through a mesh process. The reflective material layer  162   c  can be filled into the openings  202  randomly through the mesh pattern  200  to form on the second transparent conductive layer  140  the light reflecting structure  150   k  having the texture structure P 2 . Owing to the texture structure P 2  of the light reflecting structure  150   k , the opportunity for the light beam L 1  to be reflected and scattered in thin-film solar cell  100   k  can get increased. This prolongs the light path of the light beam L 2  in the photovoltaic layer  130  and, consequently, increases the opportunity for the light beam L 2  to be absorbed by the photovoltaic layer  130  to generate more electron-hole pairs. In this way, the thin-film solar cell  100   k  can effectively enhance the utilization factor of the light beam L 1 , thus resulting in higher photoelectric conversion efficiency thereof. 
       FIGS. 13A to 13D  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention. The process of forming the thin-film solar cell  100   l  is similar to that of forming the thin-film solar cell  100   k , and differences therebetween will be described below. 
     Referring to  FIG. 13A , after the second transparent conductive layer  140  is formed, a transparent material layer  164  is formed on the second transparent conductive layer  140  entirely. Then, as shown in  FIG. 13B , a mold M 2  having the mesh pattern  200  is impressed onto the transparent material layer  164 . Next, as shown in  FIG. 13C , after curing of the transparent material layer  164   b , the mold M 2  is removed to form a mesh pattern  200  on the surface of the transparent material layer  164   b . Afterwards, as shown in  FIG. 13D , a reflective material layer  166  is formed on the transparent material layer  164   b . The reflective material layer  166  covers the entire transparent material layer  164   b  and portions of the second transparent material layer  140 . Here, the stack structure formed by the transparent material layer  164   b  and the reflective material layer  166  can be viewed as a light reflecting structure  150   l . Then, as shown in  FIG. 13D , the adhesive layer  170  is applied onto the light reflecting structure  150   l  to package the counter transparent substrate  180  and the transparent substrate  110  together, thus completing the fabrication of the thin-film solar cell  100   l.    
       FIGS. 14A to 14E  are schematic cross-sectional views illustrating a manufacturing process of a thin-film solar cell according to another embodiment of the present invention. The process of forming the thin-film solar cell  100   m  is similar to that of forming the thin-film solar cell  100   k , and differences therebetween will be described below. 
     Referring to  FIG. 14A , after the second transparent conductive layer  140  is formed, a first mold M 3  having a first mesh pattern  210  is disposed on the second transparent conductive layer  140 . The first mesh pattern  210  has a plurality of openings  212  exposing the second transparent conductive layer  140 . Next, as shown in  FIG. 14B , a first sub-pattern structure  152   b  is formed on the first mold M 3 , with the first sub-pattern structure  152   b  being connected with portions of the second transparent conductive layer  140 . Next, as shown in  FIG. 14C , after curing of the first sub-pattern structure  152   b , the first mold M 3  is removed and a second mold M 4  having a second mesh pattern  220  is disposed on the first sub-pattern structure  152   b . The second mesh pattern  220  has a plurality of second openings  222  that expose at least portions of the first openings  212 . Thereafter, as shown in  FIG. 14D , a second sub-pattern structure  154   b  is formed on the first sub-pattern structure  152   b . The second sub-pattern structure  154   b  at least partially overlaps the first sub-pattern structure  152   b  to form a light reflecting structure  150   m . Finally, as shown in  FIG. 14E , the adhesive layer  170  is applied onto the light reflecting structure  150   m  to package the counter transparent substrate  180  and the transparent substrate  110  together, thus completing the fabrication of the thin-film solar cell  100   m.    
     Of course, the aforesaid methods for manufacturing thin-film solar cells are only illustrated as examples, and some of the steps are common in the art. Depending on practical conditions, alterations, omissions or additions may be made on the steps by those skilled in the art to meet practical process requirements, which will not be further described herein. Furthermore, in other embodiments not shown, the aforesaid elements can be optionally selected by those skilled in the art, based on the descriptions of the aforesaid embodiments, to achieve the desired technical effect depending on practical requirements. 
     According to the above descriptions, the methods for manufacturing a thin-film solar cell of the present invention form a light reflecting structure having a texture structure on the second transparent conductive layer to increase the opportunity for the light beam to be reflected in the thin-film solar cell. This can prolong the light path of the light beam in the photovoltaic layer so that the light beam will be more likely absorbed by the photovoltaic layer to generate more electron-hole pairs. In other words, the methods for manufacturing a thin-film solar cell of the present invention can effectively enhance the utilization factor of the light beam to improve the photoelectric conversion efficiency of the resulting thin-film solar cell. 
     The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.