Abstract:
A single-sided dye-sensitized solar cell having a vertical patterned structure is disclosed. A patterned nonconductive insulating layer is formed directly over first portions of a conductive substrate. An electrocatalyst material layer is formed directly over second portions of the conductive substrate, where the second portions of the conductive substrate do not overlap with the first portions of the conductive substrate. A second conductive layer is formed directly over the patterned nonconductive insulating layer and a porous layer is formed directly over the second conductive layer. An electrolyte is formed over the porous layer and the electrocatalyst material layer and a transparent sheet is formed over the electrolyte.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/347,432, filed on May 23, 2010, which is incorporated herein by reference in its entirety. 
     
    
     SPONSORSHIP STATEMENT 
       [0002]    This application has been sponsored by the Iranian Nanotechnology Initiative Council and the Sharif University of Technology, which do not have any rights in this application. 
       TECHNICAL FIELD 
       [0003]    This application generally relates to dye-sensitized solar cells, and more particularly relates to single-sided dye-sensitized solar cells having a vertical patterned structure. 
       BACKGROUND 
       [0004]    A dye-sensitized solar cell (hereinafter “DSC”) is a photoelectrochemical cell that converts solar energy into electrical power. An example structure of a conventional DSC is illustrated in  FIG. 1 . The conventional DSC includes a mesoporous layer  12  made up of a large bandgap semiconductor material, which is sensitized using a monolayer of an appropriate dye that acts as a photo-anode. The mesoporous layer  12  is deposited on a glass substrate  10  with a transparent conducting oxide (hereinafter “TCO”) layer  11 , such as, for example, fluorine-doped tin oxide (hereinafter “FTO”). A counter electrode can be made up of a FTO layer  16  deposited on another glass substrate  17  and adjacent to a thin layer  15  made up of, for example, platinum (Pt) or carbon (C). The TCO layer  11  and the thin layer  15  are separated by, for example, about  50  μm and sealed on the sides by spacers  13 . 
         [0005]    The volume between the TCO layer  11  and the thin layer  15  is filled with an electrolyte  14  that can include, for example, I − /I 3   −  redox species. The dye molecules adsorbed on the surface of the mesoporous layer  12  act to absorb light photons and inject the resulting excited electrons to the mesoporous layer  12 , resulting in electrical power production within the DSC. 
         [0006]    Since the first DSC structure was introduced in the early 1990s, many efforts have been made to enhance the efficiency and reduce the fabrication costs of the cells. Currently, DSC efficiency measured in laboratories has improved from 7% to about 12%, which is below the efficiency of silicon and thin film solar cells. While research to improve the efficiency of DSCs is continuing, efforts are also being made to reduce fabrication costs by replacing components within a DSC with a more readily available, lower priced components. 
         [0007]    A considerable fraction, up to about 25%, of the fabrication costs of a DSC is due to the FTO glass used. Moreover, FTO glass poses limitations in the fabrication of DSCs, due to its limited conductivity and transparency. The conductivity and transparency in FTO glass are inversely related, i.e., the higher the conductivity, the lower the transparency and vice-versa. Typically, the resistivity of FTO glass is about 8 Ω/cm 2 . In the case of DSCs tested in a laboratory that are a few millimeters in size, this resistivity does not greatly impact the performance of the DSCs. However, in large modules, the series resistance of the FTO layer may reduce the fill factor and current density of the modules. Reducing the resistivity of FTO layers may be possible by optimizing the chemical composition of the layer, as well as its thickness. However, within feasible conditions, the resistivity cannot be reduced by more than a factor of 4. By comparison, the resistivity of other metals is typically 100 times less than FTO. 
         [0008]    In addition, FTO glass is not fully transparent. At least some, typically about 25%, of the light incident on FTO glass is reflected and, thus, not absorbed. Less light must be reflected to increase the efficiency of DSCs in the future. 
         [0009]    Also, in a conventional DSC structure, an electrolyte  14  or a hole conductive layer provides electrical conductance between the working and counter electrodes. Acetonitrile electrolytes, which use I − /I 3   −  as the redox couple, are common electrolytes that provide high performance. In these electrolytes, diffusion of the I 3   −  species limits ion conductivity at high current densities. The limitations posed by such diffusion are critical, as the diffusion forces use of low viscosity electrolytes with relatively high vapor pressures. The evaporation of low viscosity electrolytes can lead to short cell life. 
         [0010]    The distance between the electrodes is controlled by the spacers  13  that seal the DSC. Due to ion diffusion, it is also important that the distance between the working and counter electrodes be as short as possible. However, in conventional DSCs, the distance between the two electrodes cannot be lower than a certain level due to possible contact between the electrodes, resulting in short-circuiting. 
       SUMMARY 
       [0011]    A single-sided dye-sensitized solar cell having a vertical patterned structure is disclosed. A patterned nonconductive insulating layer is formed directly over first portions of a conductive substrate. An electrocatalyst material layer is formed directly over second portions of the conductive substrate, where the second portions of the conductive substrate do not overlap with the first portions of the conductive substrate. A second conductive layer is formed directly over the patterned nonconductive insulating layer and a porous layer is formed directly over the second conductive layer. An electrolyte is formed over the porous layer and the electrocatalyst material layer and a transparent sheet is formed over the electrolyte. 
         [0012]    In some implementations, the single-sided dye-sensitized solar cell can include two or more spacers located between the conductive substrate and the transparent sheet at opposite ends of the single-sided dye-sensitized solar cell. The volume between the two or more spacers, the conductive substrate, and the transparent sheet can include the electrolyte. 
         [0013]    In some implementations, the first portions of the conductive substrate and the second portions of the conductive substrate can be interdigitated. The conductive substrate can include one or more conductive materials selected from the group consisting of copper, nickel, chromium, titanium, stainless steel, and silicon. The patterned nonconductive insulating layer can include one or more nonconductive insulating materials selected from the group consisting of silicon oxides, silicon nitride, zirconium oxide, and aluminum oxide. The patterned nonconductive insulating layer can include one or more polymers. 
         [0014]    In some implementations, the porous layer can include one or more of titanium dioxide and/or zinc oxide. The titanium dioxide can include titanium dioxide nanoparticles and the zinc oxide can include zinc oxide nanoparticles. The porous layer can include one or more dye sensitizers and/or quantum dot sensitizers. 
         [0015]    In some implementations, the electrocatalyst material layer can include one or more electrocatalyst materials selected from the group consisting of platinum and cobalt sulfide. The second conductive layer can include one or more conductive materials selected from the group consisting of copper, nickel, chromium, titanium, and stainless steel. 
         [0016]    In some implementations, the thickness of the second conductive layer can range from 100 nm to 100 μm, the width of the patterned nonconductive insulating layer, the second conductive layer, and the porous layer can range from 10 μm to 100 μm, and the width of the electrocatalyst material layer can range from 5 μm to 100 μm. The width of the patterned nonconductive insulating layer, the second conductive layer, and the porous layer can be greater than the width of the electrocatalyst material layer. 
         [0017]    Another single-sided dye-sensitized solar cell having a vertical patterned structure is also disclosed. A photo-anode is formed including a patterned nonconductive insulating layer formed directly over first portions of a conductive substrate, a second conductive layer formed directly over the patterned nonconductive insulating later, and a porous layer formed directly over the second conductive layer. A cathode is formed including an electrocatalyst material layer formed directly over second portions of the conductive substrate, wherein the second portions of the conductive substrate do not overlap with the first portions of the conductive substrate. An electrolyte is formed over the photo-anode and the cathode and a transparent sheet is formed over the electrolyte. 
         [0018]    Details of one or more implementations of the single-sided dye-sensitized solar cells having a vertical patterned structure are set forth in the accompanying drawings and the description below. Other aspects that can be implemented will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  illustrates the structure of a conventional DSC. 
           [0020]      FIG. 2   a  illustrates the structure of an implementation of a DSC having two electrodes separated vertically on a single side of the cell. 
           [0021]      FIG. 2   b  illustrates a three-dimensional perspective view of the DSC illustrated in  FIG. 2   a  showing two vertically-separated electrodes. 
           [0022]      FIG. 3   a  illustrates the structure of an implementation of a DSC having two electrodes separated horizontally on a single side of the cell. 
           [0023]      FIG. 3   b  is a top view of the DSC illustrated in  FIG. 3   a  showing two horizontally-separated electrodes. 
       
    
    
       [0024]    Like reference symbols indicate like elements throughout the specification and drawings. 
       DETAILED DESCRIPTION 
       [0025]    A new structure of a DSC that includes two vertically separated electrodes on a single side of the cell is disclosed. By including the working and counter electrodes on a single side of the cell, this structure eliminates the need for TCO glass within a DSC, leading to a considerable reduction in fabrication costs. 
         [0026]    In one implementation, two electrodes of a DSC are patterned to be separated vertically. As illustrated in  FIGS. 2   a - 2   b , for example, a DSC  100  includes a conductive substrate  20 , acting as one electrode, and a patterned metal layer  22 , acting as the other electrode, separated by a nonconductive insulating material  21 . The pattern of nonconductive insulating material  21  can be in the form of fingers that are to be interdigitated with an electrocatalyst material  3 , as illustrated in  FIG. 2   a . In some implementations, the nonconductive insulating material  21  can be patterned identically to the patterned metal layer  22  to create an insulating layer between the conductive substrate  20  and the patterned metal layer  22 . In other implementations, the nonconductive insulating material  21  can be patterned differently from the pattern metal layer  22 , so that the nonconductive insulating material  21  and the pattern metal layer  22  do not completely overlap. 
         [0027]    A porous layer  2 , which can include, for example, titanium dioxide (TiO 2 ) and/or zinc oxide (ZnO), is deposited on one of the electrodes, such as the patterned metal layer  22 . The titanium dioxide and/or zinc oxide particles in the porous layer  2  can be nanoparticles, i.e., particles that have an average size of less than 100 nm. A site-selective deposition method is used to deposit the porous layer  2 , such as, for example, electrochemical deposition and electrophoretic deposition (hereinafter “EPD”). 
         [0028]    The porous layer  2  can be loaded with one or more dye sensitizers and/or quantum dot sensitizers, such as, for example, N719, N3, black dye, and/or TT1 to act as a photo-anode. In some implementations, the dye sensitizers can be adsorbed on the surface of the porous layer  2  by soaking the porous layer  2  in a dye solution including the one or more dye sensitizers. In other implementations, a paste of semiconductor nanoparticles including the one or more dye sensitizers can be applied to the surface of the porous layer  2  by, for example, screen printing and/or doctor blade techniques. 
         [0029]    The other electrode, such as the conductive substrate  20 , is coated with an electrocatalyst material  3 , which can be made up of, for example, platinum (Pt) or cobalt sulfide (CoS), to act as the cathode. The electrocatalyst material  3  is deposited in an interdigitated manner between the fingers of the nonconductive insulating material  21 . A transparent sheet  24 , which can be made of, for example, glass or plastic, is located opposite the conductive substrate  20  with spacers  23  located in-between at opposite ends of the DSC  100 . The volume within the transparent sheet  24 , spacers  23 , and conductive substrate  20  can be filled with an electrolyte  5 . 
         [0030]    The conductive substrate  20  can be a polished metal sheet, a foil of a metal, or an insulating substrate coated with a metal layer. In some implementations, the conductive material can be one of more of, for example, copper (Cu), nickel (Ni), chromium (Cr), titanium (Ti), stainless steel, and/or silicon wafer. The metal can be selected based on the parameters of fabrication, such as compatibility with the electrochemical deposition process used to fabricate the DSC  100  and/or the metal&#39;s resistance to thermal or chemical degradation. 
         [0031]    The nonconductive insulating material  21  on the conductive substrate  20  can be deposited by vapor deposition methods, such as, for example, evaporation, sputtering, and/or chemical vapor deposition; by chemical treatment, such as, for example, thermal oxidation and/or plasma nitridation; and/or by electrochemical methods, such as, for example, EPD. The type and thickness of the nonconductive insulating material  21  can be chosen to provide sufficient insulation between the conductive substrate  20  and the patterned metal layer  22 , and remain stable during fabrication and in working conditions. The nonconductive insulating material  21  can include, for example, one or more of silicon oxides (SiO 2 ; SiO), silicon nitride (Si 3 N 4 ), zirconium oxide (ZrO 2 ), and/or aluminum oxide (Al 2 O 3 ). In some implementations, the nonconductive insulating material  21  can include one or more polymers. 
         [0032]    The patterned metal layer  22  is deposited on the nonconductive insulating material  21  using any physical or chemical deposition method. The patterned metal layer  22  can be made up of one or more of, for example, copper (Cu), nickel (Ni), chromium (Cr), titanium (Ti), and/or stainless steel. The thickness of the patterned metal layer  22  can range from 100 nm to 100 μm. In some implementations, the patterned metal layer  22  and the nonconductive insulating material  21  can both be patterned in the interdigitated pattern illustrated in  FIG. 2   b , while in other implementations the patterned metal layer  22  and the nonconductive insulating material  21  can be patterned in another pattern. 
         [0033]    The width of the channels including the electrocatalyst material  3  between the fingers of the nonconductive insulating material  21  and patterned metal layer  22  can range from 5 μm to 100 μm, and preferably being about 5 μm. In some implementations, the width of the channels including the electrocatalyst material  3  can be the same as the width of the nonconductive insulating material  21 , whereas in other implementations, the width of the channels including the electrocatalyst material  3  can be different from, and preferably smaller than, the width of the nonconductive insulating material  21 . 
         [0034]    The spacers  23  are placed between the conductive substrate  20  and the transparent sheet  24 . The spacers  23  can be made up of one or more thermoplastic polymers, such as, for example, anhydride-modified ethylene vinyl acetate polymers. 
         [0035]    In another implementation, two electrodes of a DSC are patterned to be separated horizontally. As illustrated in  FIGS. 3   a  and  3   b , DSC  200  includes two finger patterns that are interwoven, i.e., in an interdigitated pattern. Each finger pattern can act as an electrode, with one finger pattern acting as an anode and its adjacent finger pattern acting as a cathode. An interdigitated metal layer  31  is patterned on an insulating substrate  30  to provide two horizontally-separated, interdigitated electrodes. The interdigitated metal layer  31  can be made up of one or more of, for example, copper (Cu), nickel (Ni), chromium (Cr), titanium (Ti), and/or stainless steel. The insulating substrate  30  can be made up of, for example, glass or plastic. The spacing between the adjacent fingers of the interdigitated metal layer  31  should be as small as possible to provide low cathode-anode electrolytic resistance, while retaining adequate insulation between the electrodes. In some implementations, for example, the spacing between the adjacent fingers of the interdigitated metal layer  31  can range between 5-100 μm. 
         [0036]    A porous layer  2 , which can include, for example, titanium dioxide (TiO 2 ) or zinc oxide (ZnO), is deposited on one of the horizontally-separated, interdigitated electrodes of the interdigitated metal layer  31 . The porous layer  2  can be loaded with a dye sensitizer to act as a photo-anode. The other of the horizontally-separated, interdigitated electrodes of the interdigitated metal layer  31  can be coated with an electrocatalyst material  3 , which can be made up of, for example, platinum (Pt) or cobalt sulfide (CoS), to act as the cathode. 
         [0037]    A transparent sheet  33 , which can be made of, for example, glass or plastic, is located opposite the insulating substrate  30  with spacers  23  located in-between at opposite ends of the DSC  200 . The volume within the transparent sheet  33 , spacers  32 , and insulating substrate  30  can be filled with an electrolyte  5 . 
         [0038]    In both the vertical and horizontal electrode implementations disclosed above, light harvesting can be improved if a majority of the area on the substrate is covered by the photo-anode electrode rather than the cathode electrode. For example, referring to  FIGS. 2   a  and  2   b , the width of photo-anode fingers  20 - 22  can be wider than the width of cathode fingers  3 . For example, the width of the photo-anode fingers  20 - 22  can range from 10-100 μm and the width of the cathode fingers can range from 5-100 μm. In some implementations, referring the  FIGS. 3   a  and  3   b , the width of photo-anode fingers  2 ,  31  can be wider than the width of cathode fingers  3 ,  31 . However, in other implementations, the width of the photo-anode fingers  2 ,  31  and cathode fingers  3 ,  31  can be the same. 
         [0039]    Moreover, the width of the cathode fingers in both the DSC  100  having the vertical electrode structure and the DSC  200  having he horizontal electrode structure, and the space between the photo-anode and cathode fingers in the DSC  200  should be minimized. One limitation in the minimization of the width of the cathode fingers and the space between the photo-anode and cathode fingers is the current capability to pattern fine structures on large areas. Whereas submicron lithography is now a routine in microelectronics, submicron lithography poses many challenges in the fabrication of large solar cells. 
         [0040]    As such, in some implementations, the width between the fingers of the interdigitated metal layer  31  of the DSC  200  can be, for example, 5 μm. Smaller spacing may cause short circuiting, as the porous layer  2 , having a thickness of about 10 μm and acting as the photo-anode, may grow laterally during deposition and make contact with the cathode. The width of the photo-anode fingers can range from about 10 μm to 100 μm, such as, for example, 20 μm for acetonirtile-based electrolytic cells. 
         [0041]    In some implementations, photolithography can be used to pattern both the DSC  100  having the vertical electrode structure and the DSC  200  having the horizontal electrode structure. The photoresist layer can be applied by various methods, such as, for example, exposure, development and etching. 
         [0042]    In other implementations, other techniques can be used to define the interdigitated pattern on the conductive substrate. For example, mechanical methods, such as mechanical scratching can be used to separate neighboring fingers from one another. Mechanical scratching can be performed by, for example, a sharp diamond tip that travels on the surface of a substrate and excavates the substrate. In other examples, a focused laser beam that creates a high, local temperature on the surface of the substrate can be used to create channels as the beam moves along the surface. 
         [0043]    In yet other examples, a shallow scratch on a conductive substrate can be created at the separation lines, followed by chemical and/or electrochemical etching of the metal. The etching can be continued until electrical contact between two adjacent fingers completely disappears since etching takes place more readily on the scratched areas. This mechano-chemical method is more controllable relative to the mechanical methods disclosed above, as the electrical contact between two adjacent fingers can be monitored during the etching process. 
         [0044]    In examples where the porous layer  2  includes zinc oxide (ZnO), the zinc oxide layers can be formed on a conductive substrate in aqueous solutions. The morphology of the layers can be controlled by adding certain adsorbing ions in the electrolyte to realize structures of wires, rods, plates, or other morphologies. It is possible to grow crystalline ZnO porous layers by electrochemical deposition, which does not require any further heat treatment for crystallization. 
         [0045]    In examples where the porous layer  2  includes titanium dioxide (TiO 2 ), electrochemical growth is typically performed on organic electrolytes. However, titanium dioxide usually requires post treatment at temperatures ranging from about 400° C. to 550° C. to enhance crystallinity. Post treatment is essential to reduce the trap states in the material. 
         [0046]    It is to be understood the implementations are not limited to the particular processes, devices, and/or apparatus described which may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used in this application, the singular forms “a”, “an” and “the” include plural referents unless the content clearly indicates otherwise. 
         [0047]    Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment herein. The appearances of the phrase “in some embodiments” in the specification do not necessarily all refer to the same embodiment. 
         [0048]    Accordingly, other embodiments and/or implementations are within the scope of this application.