Abstract:
A polymer solar cell is provided. The polymer solar cell includes a cathode and an anode, an active layer having a first surface and a second surface disposed between the cathode and the anode, and a titanium dioxide layer formed on one of the first and second surfaces of the active layer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority of Taiwan Patent Application No. 97141558, filed on Oct. 29, 2008, the entirety of which is incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a polymer solar cell, and more particularly to a polymer solar cell coated with a titanium dioxide layer. 
         [0004]    2. Description of the Related Art 
         [0005]    Compared to chip-type solar cells and thin-film solar cells, a polymer solar cell possesses higher efficiency at a lower cost. With reliability and efficiency thereof further improved, the application of polymer solar cell is expected to increase. 
         [0006]    An active layer of a polymer solar cell comprises a p-n material such as poly(3-hexylthiophene) (P3HT)/(6,6)-phenyl C61-butyric acid methyl ester (PCBM). Such active layer materials possess low cost, light weight, flexibility and a potential for application in large-area device fabrication. 
         [0007]    However, such active layer polymer materials are easily damaged by sunlight (ultraviolet, 250-400 nm), deteriorating cell efficiency and reducing lifespan. Thus, development of a polymer solar cell capable of protecting the active layer polymer materials from ultraviolet damage is desirable. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    One embodiment of the invention provides a polymer solar cell comprising a cathode and an anode, an active layer having a first surface and a second surface disposed between the cathode and the anode and a titanium dioxide layer formed on one of the first surface and the second surface of the active layer. 
         [0009]    A modified titanium dioxide nano crystal is coated on an active layer of a polymer solar cell through a solution process to protect the active layer, effectively improving cell stability and lifespan. 
         [0010]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawing, wherein: 
           [0012]      FIG. 1  is a cross-sectional view of a polymer solar cell according to an embodiment of the invention. 
           [0013]      FIG. 2  shows a comparison of cell efficiency between a polymer solar cell provided by the invention and a conventional polymer solar cell. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0015]    Referring to  FIG. 1 , a polymer solar cell in an embodiment of the invention is disclosed. A polymer solar cell  10  comprises a composite anode  12 , an active layer  18 , a titanium dioxide layer  20  and a composite cathode  22 . The active layer  18  is disposed between the composite anode  12  and the composite cathode  22 . The titanium dioxide layer  20  is formed on the active layer  18 . 
         [0016]    The composite anode  12  comprises an anode  14  and a material layer  16  coated thereon. The anode  14  may be an ITO glass. The material layer  16  may comprise conductive polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) or poly(styrene sulfonate) (PSS). 
         [0017]    The active layer  18  may comprise polymer semiconductors such as poly(3-hexylthiophene) (P3HT) or poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and fullerene derivatives such as (6,6)-phenyl C61-butyric acid methyl ester (PCBM). 
         [0018]    The titanium dioxide layer  20  may comprise titanium dioxide-containing nano structures. The titanium dioxide-containing nano structure may comprise a titanium dioxide crystal and a compound formed on the surface thereof. The titanium dioxide crystal may be an anatase titanium dioxide crystal, with a size of 18-22 nm×2-6 nm. The compound may comprise carboxyl-containing compounds or phosphonate-containing compounds. The carboxyl-containing compound may comprise C18 acidic compounds such as oleic acid. The phosphonate-containing compound may comprise surfactants such as diethyl(2-cyanoethyl)phosphonate, diethyl(2-oxopropyl)phosphonate, triethyl-3-phosphonopropionate or diethyl(2-oxo-2-phenylethyl)phosphonate or polymer compounds having the formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    The composite cathode  22  comprises a material layer  24  and a cathode  26  formed thereon. The material layer  24  may comprise LiF. The cathode  26  may comprise aluminum. 
         [0019]    A modified titanium dioxide nano crystal is coated on an active layer of a polymer solar cell through a solution process to protect the active layer, effectively improving cell stability and lifespan. 
       EXAMPLE 1  
       [0020]    Preparation of a Titanium Dioxide-Containing Nano Structure (1) 
         [0021]    (1) Synthesis of titanium dioxide-oleic acid 
         [0022]    78 ml oleic acid was added to a 250 ml reaction bottle. Nitrogen gas was then conducted thereinto through a needle. Next, the reaction bottle was heated to 120° C. to remove water. After reaction for 1 hour, the temperature was cooled to 100° C. and the needle was removed. 2.95 ml titanium (IV) isopropoxide (TTIP) was then added. Next, a trimethylamine-N-oxide (TMAO) aqueous solution (2.22 g TMAO was dissolved in 10ml water) was added to react for 6 hours. After cooling to room temperature, 200 ml methanol was added and a centrifugation was processed. After washing with methanol for several times and drying, 1.2 g titanium dioxide-oleic acid was obtained. 
         [0023]    (2) Synthesis of titanium dioxide-oleic acid/diethyl(2-cyanoethyl)phosphonate 
         [0024]    0.2 g titanium dioxide-oleic acid, 0.1 g diethyl(2-cyanoethyl)phosphonate and 2 ml chlorobenzene were added to a 50 ml reaction bottle. After the titanium dioxide was completely dissolved in solvent through ultrasonic vibration, the reaction bottle was heated under 100° C. for 24 hours. After removal of solvent, a titanium dioxide-containing nano structure of titanium dioxide-oleic acid/diethyl(2-cyanoethyl) phosphonate was prepared. 
       EXAMPLE 2  
       [0025]    Preparation of a Titanium Dioxide-Containing Nano Structure (2) 
         [0026]    (1) Synthesis of titanium dioxide-oleic acid 
         [0027]    78 ml oleic acid was added to a 250 ml reaction bottle. Nitrogen gas was then conducted thereinto through a needle. Next, the reaction bottle was heated to 120° C. to remove water. After reaction for 1 hour, the temperature was cooled to 100° C. and the needle was removed. 2.95 ml titanium (IV) isopropoxide (TTIP) was then added. Next, a trimethylamine-N-oxide (TMAO) aqueous solution (2.22 g TMAO was dissolved in 10 ml water) was added to react for 6 hours. After cooling to room temperature, 200 ml methanol was added and a centrifugation was processed. After washing with methanol for several times and drying, 1.2 g titanium dioxide-oleic acid was obtained. 
         [0028]    (2) Synthesis of titanium dioxide-oleic acid/P4K 
         [0029]    0.2 g titanium dioxide-oleic acid, 0.1 g 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and 2 ml THF were added to a 50 ml reaction bottle. After the titanium dioxide was completely dissolved in solvent through ultrasonic vibration, the reaction bottle was heated under 60° C. for 18 hours. After removal of solvent, a titanium dioxide-containing nano structure of titanium dioxide-oleic acid/P4K was prepared. 
       EXAMPLE 3  
       [0030]    Preparation of a Polymer Solar Cell (1) 
         [0031]    An ITO glass was washed with water, acetone and isopropanol respectively for 15 min. After applying plasma for 5 min, a material layer (PEDOT/PSS) was coated thereon with a thickness of 30 nm. The ITO glass with the PEDOT/PSS material layer was then heated at 80° C. for 10 min to prepare a composite anode. Next, P3HT and PCMB were dissolved in chlorobenzene with a weight ratio of 1:0.6 to prepare a solution, with continuous stirring for 24 hours (in a glove box). The solution was then coated on the PEDOT/PSS material layer with a thickness of 90-120 nm. After sitting for 8 hours (overnight), an active layer was prepared. Next, a 0.1 wt % anatase titanium dioxide solution (prepared by Example 1) was coated on the active layer with a rotation rate of 5,000 rpm to prepare a titanium dioxide layer. 5 Å LiF layer and 1,000 Å aluminum layer were then evaporated on the titanium dioxide layer to prepare a composite cathode. After annealing at 158° C. for 8 min, the product was packaged by UV gel. A polymer solar cell was prepared. The efficiency thereof was tested using an AM1.5 G, 1 sun light source. The efficiency was 3.59%. 
       EXAMPLE 4  
       [0032]    Preparation of a Polymer Solar Cell (2) 
         [0033]    An ITO glass was washed with water, acetone and isopropanol respectively for 15 min. After applying plasma for 5 min, a material layer (PEDOT/PSS) was coated thereon with a thickness of 30 nm. The ITO glass with the PEDOT/PSS material layer was then heated at 80° C. for 10 min to prepare a composite anode. Next, P3HT and PCMB were dissolved in chlorobenzene with a weight ratio of 1:0.6 to prepare a solution, with continuous stirring for 24 hours (in a glove box). The solution was then coated on the PEDOT/PSS material layer with a thickness of 90-120 nm. After sitting for 8 hours (overnight), an active layer was prepared. Next, a 0.1 wt % anatase titanium dioxide solution (prepared by Example 2) was coated on the active layer with a rotation rate of 5,000 rpm to prepare a titanium dioxide layer. 5 Å LiF layer and 1,000 Å aluminum layer were then evaporated on the titanium dioxide layer to prepare a composite cathode. After annealing at 158° C. for 8 min, the product was packaged by UV gel. A polymer solar cell was prepared. The efficiency thereof was tested using an AM1.5 G, 1 sun light source. The efficiency was 2.48%. 
         [0034]      FIG. 2  shows a comparison of cell efficiency between the polymer solar cell prepared by Example 3 and a conventional polymer solar cell. 
         [0035]      FIG. 2  indicates that the efficiency of the polymer solar cell coated with a modified titanium dioxide layer on the active layer prepared by Example 3 is apparently higher than the conventional polymer solar cell without the coated a titanium dioxide layer due to the polymer materials protecting the active layer from damage. 
         [0036]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.