Abstract:
The present invention provides a high efficiency colored solar cell, which exhibits both a high conversion efficiency and optically desirable color, comprising a photoelectric conversion substrate; at least one anti-reflection layer formed on the photoelectric conversion substrate; and two or more transparent inorganic dielectric layers formed on the anti-reflection layer(s), wherein the transparent inorganic dielectric layers include at least one layer containing an oxide of titanium. The subject invention also provides a panel comprising the above-mentioned high efficiency colored solar cell.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related to a colored solar cell which exhibits both a high conversion efficiency and an optically desirable color. The present invention is also related to a panel containing said solar cell and the process for preparing the solar cell. 
       BACKGROUND OF THE INVENTION 
       [0002]    Due to the diminishing amount of fossil fuel and the environmental problems associated therewith, there is an urging need in the industry to find an efficient and environmentally friendly alternative energy source, and among various alternative energy sources, solar energy provides a potential solution to such crisis. A solar cell, which is also called a photovoltaic cell, is a device which converts the light energy from the sun into electricity via the photoelectric effect. A crystalline silicon solar cell is one of the prevalently used types of the solar cells. The design of a crystalline silicon solar cell is based on the formation of a p/n junction on the light incident plane and the formation of an anti-reflection layer on the junction to reduce the reflection of photons. In order to reduce the reflectivity and enhance the overall conversion efficiency, the appearance of the crystalline silicon solar cell or the panel is only limited to blue color. However, such monotonous color does not appear appealing to the public when the governments of many countries promote the installation of solar cells or solar cell panels on the roof or outer walls of buildings. A more pleasing color which is not only scientifically highly efficient but also aesthetically decorative to the buildings is needed, and development of solar cells or solar cell panels having various colors for fitting into the buildings or the environment has to be carried out. Japanese patent publication JP 2003/197937 A discloses that solar cells exhibiting various colors may be achieved by disposing another anti-reflection layer on an existing anti-reflection layer on the surface of the solar cell and adjusting the thickness and reflectivity of said another anti-reflection layer. Nevertheless, the color of the solar cell is susceptible to the reflectivity and thickness of the anti-reflection layers, and the conversion efficiency of the solar cell will be directly affected by the selected materials of the anti-reflection layers. Due to the great amount of the potential species of materials and the extent of possible ranges of thickness, finding a suitable combination of the materials and thicknesses for such color adjusting measure is not only complicated but also time-consuming. In the prior art, the conversion efficiency of solar cells and the appearance of the solar cells other than conventional blue is often a trade-off, which holds the colored solar cells back from being commercialized successfully. Moreover, the color of a solar cell can still be changed during the encapsulation into a solar cell panel for further applications, for example, by the protection layer disposed thereon. 
         [0003]    Given the aforementioned problems left in the prior art, the objective of the present invention is to provide a colored solar cell which exhibits both a high conversion efficiency and an optically desirable color, and to provide an easy-to-produce colored solar cell and a panel containing the same to achieve the popularization of solar cells. 
       SUMMARY OF THE INVENTION 
       [0004]    In order to achieve the aforementioned objective, the present invention provides a colored solar cell comprising a photoelectric conversion substrate; at least one anti-reflection layer formed on the photoelectric conversion substrate; two or more transparent inorganic dielectric layers which are formed on the anti-reflection layer(s) and comprise at least one first transparent inorganic dielectric layer consisting of an oxide of titanium. 
         [0005]    In another aspect, the present invention provides a solar cell panel, comprising a colored solar cell module formed from the colored solar cell according to the present invention; a protection layer disposed on the colored solar cell module; and a transparent glass plate disposed on the protection layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  shows the profile of a colored solar cell according to the present invention. 
           [0007]      FIG. 2  shows the profile of a colored solar cell according to the present invention. 
           [0008]      FIG. 3  shows the profile of a colored solar cell according to the present invention. 
           [0009]      FIG. 4(   a ) shows the reflectivity of a red solar cell according to the present invention at various wavelengths. 
           [0010]      FIG. 4(   b ) shows the reflectivity of a red solar cell according to the present invention at various wavelengths. 
           [0011]      FIG. 5  shows the reflectivity of a green solar cell according to the present invention at various wavelengths. 
           [0012]      FIG. 6  shows the reflectivity of a purple solar cell according to the present invention at various wavelengths.  FIG. 7  shows the reflectivity of a red solar cell according to the present invention at various wavelengths. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Throughout this application, the term “about” is used to indicate that the specific value measured by a person skilled in the art includes inherent but acceptable variation of errors from the method being employed to determine the value. 
         [0014]    The structure of the prevalently used crystalline silicon solar cell mainly comprises (1) a photoelectric conversion substrate; and (2) an anti-reflection layer formed on the photoelectric conversion substrate, wherein the photoelectric conversion substrate comprises n-type doped and p-type doped semiconductor materials, and the semiconductor materials may be polycrystalline silicon materials or monocrystalline silicon materials. The n-type doped and p-type doped semiconductor materials are brought into contact with each other to form a photoelectric conversion substrate with a p/n junction. The anti-reflection layer may be a thin film formed from a nitride of silicon (SiN x ). 
         [0015]    The colored solar cell of the present invention comprises a photoelectric conversion substrate; at least one anti-reflection layer formed on the photoelectric conversion substrate; and two or more transparent inorganic dielectric layers which are formed on the anti-reflection layer, wherein the two or more transparent inorganic dielectric layers comprise at least one first transparent inorganic dielectric layer consisting of an oxide of titanium. 
         [0016]    In one embodiment of the present invention, the present invention provides a colored solar cell comprising a photoelectric conversion substrate; at least one anti-reflection layer formed on the photoelectric conversion substrate; and two transparent inorganic dielectric layers formed on the anti-reflection layer, wherein one of the two transparent inorganic dielectric layers is a first transparent inorganic dielectric layer comprising an oxide of titanium and the other one is a second transparent inorganic dielectric layer. 
         [0017]    In reference to  FIG. 1  showing the profile of a colored solar cell of the present invention, the colored solar cell comprises a photoelectric conversion substrate (S); an anti-reflection layer (AR), which is formed on the photoelectric conversion substrate; a first transparent inorganic dielectric layer ( 11 ) consisting of an oxide of titanium and a second transparent inorganic dielectric layer ( 12 ). 
         [0018]    According to another embodiment of the present invention, the colored solar cell comprises a photoelectric conversion substrate; at least one anti-reflection layer formed on the photoelectric conversion substrate; at least three transparent inorganic dielectric layers formed above the anti-reflection layer and comprise at least one first transparent inorganic dielectric layer consisting of an oxide of titanium, at least one third transparent inorganic dielectric layer and at least one fourth transparent inorganic dielectric layer, wherein the first transparent inorganic dielectric layer lies between the third transparent inorganic dielectric layer and the fourth transparent inorganic dielectric layer. 
         [0019]    In reference to  FIG. 2  showing the profile of a colored solar cell according to the present invention, the colored solar cell comprises a photoelectric conversion substrate (S); an anti-reflection layer (AR) formed on the photoelectric conversion substrate; and three transparent inorganic dielectric layers formed above the anti-reflection layer. The transparent inorganic dielectric layers comprise a first transparent inorganic dielectric layer ( 11 ) consisting of an oxide of titanium, a third transparent inorganic dielectric layer ( 13 ) and a fourth transparent inorganic dielectric layer ( 14 ). The first transparent inorganic dielectric layer ( 11 ) lies between the third transparent inorganic dielectric layer ( 13 ) and the fourth transparent inorganic dielectric layer ( 14 ). 
         [0020]    According to one another embodiment of the present invention, as shown in  FIG. 3 , the colored solar cell of the present invention comprises a photoelectric conversion substrate (S); an anti-reflection layer (AR) formed on the photoelectric conversion substrate; and multiple transparent inorganic dielectric layers formed above the anti-reflection layer. The multiple transparent inorganic dielectric layers comprise two first transparent inorganic dielectric layers ( 11 ) consisting of an oxide of titanium; one third transparent inorganic dielectric layer ( 13 ); and two fourth transparent inorganic dielectric layers ( 141  and  142 ) having different transparent inorganic dielectric layer materials. The third transparent inorganic dielectric layer ( 13 ) is sandwiched by the two first transparent inorganic dielectric layers, and the two first transparent inorganic dielectric layers are respectively sandwiched by the third transparent inorganic dielectric layer and the respective fourth transparent inorganic dielectric layers. 
         [0021]    Any substrates known in the art as being suitable for solar cells may be used as the photoelectric conversion substrate of the present invention. The substrate may be a semiconductor material comprising n-type doped and p-type doped polycrystalline silicon substrates or monocrystalline silicon substrates. 
         [0022]    Any materials known in the art as being suitable for the solar cells may be used in the present invention for forming the anti-reflection layer. The anti-reflection layer may comprise a single layered SiN x  thin film formed from SiN x  or two layered SiN x  thin film with various ratios of nitrogen to silicon. The thin film may have a thickness from about 60 nm to about 100 nm. The first transparent inorganic dielectric layer of the present invention consists of an oxide of titanium and has a refractive index ranging from about 2.2 to about 2.6 and a thickness ranging from about 50 nm to about 100 nm. 
         [0023]    The second transparent inorganic dielectric layer of the present invention consists of a transparent inorganic dielectric material having a refractive index ranging from about 1.5 to about 2.0, and has a thickness from about 1 nm to 200 nm, preferably from about 100 nm to about 150 nm. The transparent inorganic dielectric material for the second transparent inorganic dielectric layer is selected from the group consisting of an aluminum doped zinc oxide, indium tin oxide, an oxide of zinc and a nitride of silicon. 
         [0024]    The third and fourth transparent inorganic dielectric layers of the present invention consist of transparent inorganic dielectric layer materials having refractive indices from about 1.5 to about 2.0 and have thicknesses from about 1 nm to about 200 nm, preferably from about 30 nm to about 100 nm. More preferably, the third transparent inorganic dielectric layer has a thickness from about 50 nm to about 100 nm, and the fourth transparent inorganic dielectric layer has a thickness from about 30 nm to about 80 nm. The transparent inorganic dielectric materials for the third and fourth transparent inorganic dielectric layers are selected from the group consisting of an aluminum doped zinc oxide, indium tin oxide, an oxide of zinc, an oxide of silicon, and a nitride of silicon. 
         [0025]    The transparent inorganic dielectric materials for the aforementioned second, third and fourth transparent inorganic dielectric layers may be the same or different. 
         [0026]    According to the present invention, the anti-reflection layer and the transparent inorganic dielectric layer may be formed by any method known in the art such as DC magnetron sputtering, RF magnetron sputtering, evaporation, sputtering, chemical vapor deposition (CVD), coating or any other methods considered to be suitable and workable by a person skilled in the art. According to one embodiment of the present invention, the colored solar cell of the present invention may be a red solar cell with a reflectivity spectrum within the visible light wavelength, which shows that the average reflectivity in the wavelength range of 600 nm to 800 nm is greater than the average reflectivity in the wavelength range of 400 nm to 600 nm by more than 35%. Further, even being encapsulated, the red solar cell of the present invention still shows a more than 25% greater average reflectivity in the wavelength range of 600 nm to 800 nm than that in the wavelength range of 400 nm to 600 nm. 
         [0027]    The present invention further provides a panel including the aforementioned solar cell which is encapsulated by sequentially disposing a protection layer and a transparent layer on the colored solar cell. The protection layer suitable for the present invention may be any known encapsulation materials in the art such as ethylene vinyl acetate (EVA), polyvinyl butyral (PVB) or any other similar materials considered to be suitable and workable by a person skilled in the art. The protection layer protects the solar cell from the exposure to water and moisture. The transparent material used in the solar cell of the present invention may be any known and suitable materials in the art, such as glass. 
         [0028]    Examples are provided below to further illustrate the present invention but not to limit the scope of the present invention. 
       EXAMPLES  
     Example 1 
       [0029]    An anti-reflection layer comprising SiN 1.1  was formed on a polycrystalline silicon photoelectric conversion substrate, and layers of an undoped zinc oxide (ZnO), titanium oxide (TiO 2 ) and indium tin oxide (ITO) were sequentially formed on the anti-reflection layer by RF magnetron sputtering to provide a red solar cell. The thicknesses and the refractive indices of the layers are listed in Table 1 below. The reflectivity of the solar cell and the solar cell panel encapsulated by EVA and a glass plate is tested at various wavelengths with a low angle incident light. The results are provided in  FIG. 4(   a ) and  FIG. 4(   b ). 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Materials 
                 Thickness 
                 Refractive index 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 ITO 
                 200 
                 nm 
                 1.8 
               
               
                   
                 TiO 2   
                 100 
                 nm 
                 2.4 
               
               
                   
                 ZnO 
                 50 
                 nm 
                 2.0 
               
               
                   
                 SiN 1.1   
                 80 
                 nm 
                 2.1 
               
               
                   
                 Polycystalline silicon (Si) 
                 0.2 
                 mm 
                 3.5 
               
               
                   
                   
               
             
          
         
       
     
         [0030]    The solar cell of Example 1 exhibits a red color due to the interferences resulting from the optical path differences produced when the incident light passes the multiple transparent inorganic dielectric layers disposed above the anti-reflection layer and reflects at each of the interfaces of the layers. 
       Example 2 
       [0031]    An anti-reflection layer comprising SiN 1.1  was formed on a polycrystalline silicon photoelectric conversion substrate, and a layer of SiN 1.3  was formed thereon by plasma-enhanced chemical vapor deposition. Layers of titanium oxide (TiO 2 ) and an aluminum-doped zinc oxide (AZO) were sequentially formed above the SiN 1.3  layer by RF magnetron sputtering. A green solar cell was obtained. The thicknesses and the refractive indices of the layers are listed in Table 2 below. The reflectivity of the solar cell and the solar cell panel encapsulated by EVA and a glass plate was tested at various wavelengths with a low angle incident light. The results are provided in  FIG. 5 . 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Materials 
                 Thickness 
                 Refractive index 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 AZO 
                 150 
                 nm 
                 1.7 
               
               
                   
                 TiO 2   
                 50 
                 nm 
                 2.4 
               
               
                   
                 SiN 1.3   
                 30 
                 nm 
                 1.9 
               
               
                   
                 SiN 1.1   
                 80 
                 nm 
                 2.1 
               
               
                   
                 Polycrystalline silicon (Si) 
                 0.2 
                 mm 
                 3.5 
               
               
                   
                   
               
             
          
         
       
     
         [0032]    The solar cell of Example 2 exhibits a green color due to the interferences resulting from the optical path differences produced when the incident light passes the multiple transparent inorganic dielectric layers disposed above the anti-reflection layer and reflects at each of the interfaces of the layers. 
       Example 3 
       [0033]    An anti-reflection layer comprising SiN 1.1  was formed on a polycrystalline silicon photoelectric conversion substrate, and layers of titanium oxide (TiO 2 ) and an aluminum-doped zinc oxide (AZO) were sequentially formed above the anti-reflection layer by RF magnetron sputtering to provide a purple solar cell. The thicknesses and the refractive indices of the layers are listed in Table 3 below. The reflectivity of the solar cell and the solar cell panel encapsulated by EVA and a glass plate was tested at various wavelengths with a low angle incident light. The results are provided in  FIG. 6 . 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Materials 
                 Thickness 
                 Refractive index 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 AZO 
                 100 
                 nm 
                 1.7 
               
               
                   
                 TiO 2   
                 50 
                 nm 
                 2.4 
               
               
                   
                 SiN 1.1   
                 80 
                 nm 
                 2.1 
               
               
                   
                 Polycrystalline silicon (Si) 
                 0.2 
                 mm 
                 3.5 
               
               
                   
                   
               
             
          
         
       
     
         [0034]    The solar cell of Example 3 exhibits a purple color due to the interferences resulting from the optical path differences produced when the incident light passes the multiple transparent inorganic dielectric layers disposed above the anti-reflection layer and reflects at each of the interfaces of the layers. 
       Example 4 
       [0035]    An anti-reflection layer comprising SiN 1.1  is formed on a polycrystalline silicon photoelectric conversion substrate, and layers of ITO, titanium oxide (TiO 2 ), an aluminum-doped zinc oxide (AZO), titanium oxide (TiO 2 ) and zinc oxide (ZnO) were sequentially formed above the anti-reflection layer by RF magnetron sputtering to provide a red solar cell. The thicknesses and the refractive indices of the layers are listed in Table 4 below. The reflectivity of the solar cell and the solar cell panel encapsulated by EVA and a glass plate was tested at various wavelengths with a low angle incident light. The results are provided in  FIG. 7 . 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Materials 
                 Thickness 
                 Refractive index 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 ZnO 
                 50 
                 nm 
                 2.0 
               
               
                   
                 TiO 2   
                 80 
                 nm 
                 2.4 
               
               
                   
                 AZO 
                 100 
                 nm 
                 1.7 
               
               
                   
                 TiO 2   
                 80 
                 nm 
                 2.4 
               
               
                   
                 ITO 
                 50 
                 nm 
                 1.8 
               
               
                   
                 SiN 1.1   
                 50 
                 nm 
                 2.1 
               
               
                   
                 Polycrystalline silicon (Si) 
                 0.2 
                 mm 
                 3.5 
               
               
                   
                   
               
             
          
         
       
     
         [0036]    The solar cell of Example 4 exhibits a red color due to the interferences resulting from the optical path differences produced when the incident light passes the multiple transparent inorganic dielectric layers disposed above the anti-reflection layer and reflects at each of the interfaces of the layers.