Abstract:
A solar cell is disclosed that may include a quantum dot, an electron conductor, and a bifunctional ligand disposed between the quantum dot and the electron conductor. The bifunctional ligand may include a first anchor group that bonds to the quantum dot and a second anchor group that bonds to the electron conductor. The solar cell may include a hole conductor that is configured to reduce the quantum dot once the quantum dot absorbs a photon and ejects an electron through the bifunctional ligand and into the electron conductor. The hole conductor may be a p-type polymer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 61/149,891 entitled “QUANTUM DOT SOLAR CELL” filed Feb. 4, 2009, the entirety of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosure relates generally to solar cells and more particularly to quantum dot solar cells. 
       SUMMARY 
       [0003]    The disclosure relates generally to solar cells. In an illustrative but non-limiting example, the disclosure relates to a solar cell that includes a quantum dot layer, an electron conductor layer, an optional bifunctional ligand layer that is disposed between the quantum dot layer and the electron conductor layer, and a polymeric hole conductor layer that is secured relative to the quantum dot layer. The polymeric hole conductor layer may include a substituted quinoline moiety. 
         [0004]    In an illustrative but non-limiting example, the disclosure relates to a solar cell that includes a quantum dot, an electron conductor and a bifunctional ligand that joins the quantum dot and the electron conductor. The illustrative solar cell also includes a hole conductor that is of the formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    where n is an integer ranging from about 6 to about 12. 
         [0005]    In another illustrative but non-limiting example, the disclosure relates to a solar cell that includes a quantum dot, an electron conductor and a hole conductor. The hole conductor may include a substituted quinoline moiety. In some cases, a bifunctional ligand may be disposed between the quantum dot and the electron conductor. In this illustrative embodiment, the bifunctional ligand may be selected from the group of 
         [0000]    
       
                 
         
             
             
         
       
     
         [0006]    The above summary is not intended to describe each disclosed embodiment or every implementation of the disclosure. The Figures and Description which follow more particularly exemplify these illustrative embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0007]    The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the disclosure. The disclosure may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which: 
           [0008]      FIG. 1  is a schematic cross-sectional side view of an illustrative but non-limiting example of a solar cell; and 
           [0009]      FIG. 2  is a schematic cross-sectional side view of another illustrative but non-limiting example of a solar cell. 
       
    
    
       [0010]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. 
       DESCRIPTION 
       [0011]    The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Although examples of construction, dimensions, and materials are illustrated for the various elements, those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized. 
         [0012]      FIG. 1  is a schematic cross-sectional side view of an illustrative solar cell  10 . In the illustrative example shown in  FIG. 1 , there may be a three-dimensional intermingling or interpenetration of the layers forming solar cell  10 , but this is not required. The illustrative solar cell  10  includes a quantum dot layer  12 . Quantum dot layer  12  may schematically represent a single quantum dot. In some cases, quantum dot layer  12  may be considered as representing a large number of individual quantum dots. In the illustrative embodiment of  FIG. 1 , a bifunctional ligand layer  14  is provided, and may schematically represent a single bifunctional ligand, such as those discussed below. In some cases, bifunctional ligand layer  14  may represent a large number of individual bifunctional ligands, with at least some of the bifunctional ligands within bifunctional ligand layer  14  bonded to corresponding quantum dots within quantum dot layer  12 . The illustrative solar cell  10  of  FIG. 1  also includes an electron conductor layer  16 . In some cases, electron conductor layer  16  may be an n-type conductor as discussed below. The illustrative solar cell  10  may further include a hole conductor layer  18 . As discussed below, the hole conductor layer  18  may be a p-type conducting electrode layer. 
         [0013]    Quantum dot layer  12  may include one quantum dot or a plurality of quantum dots. Quantum dots are typically very small semiconductors, having dimensions in the nanometer range. Because of their small size, quantum dots may exhibit quantum behavior that is distinct from what would otherwise be expected from a larger sample of the material. In some cases, quantum dots may be considered as being crystals composed of materials from Groups II-VI, III-V, or IV-VI materials. The quantum dots employed herein may be formed using any appropriate technique. Examples of specific pairs of materials for forming quantum dots include, but are not limited to, MgO, MgS, MgSe, MgTe, CaO, CaS, CaSe, CaTe, SrO, SrS,SrSe, SrTe, BaO, BaS, BaSe, BaTe, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, HgO, HgS, HgSe, HgTe, Al 2 O 3 , Al 2 S 3 , Al 2 Se 3 , Al 2 Te 3 , Ga 2 O 3 , Ga 2 S 3 , Ga 2 Se 3 , Ga 2 Te 3 , In 2 O 3 , In 2 S 3 , In 2 Se 3 , In 2 Te 3 , SiO 2 , GeO 2 , SnO 2 , SnS, SnSe, SnTe, PbO, PbO 2 , PbS, PbSe, PbTe, AN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs and InSb. 
         [0014]      FIG. 2  is a schematic cross-sectional side view of an illustrative solar cell that is similar to solar cell  10  ( FIG. 1 ). In some cases, a reflective and/or protecting layer may be disposed over the hole conductor layer, as shown. The reflective and/or protecting layer may be a conductive layer. In some instances, the reflective and/or protecting layer may include a Pt/Au/C film as both catalyst and conductor, but this is not required. Alternatively, or in addition, a flexible and optically transparent substrate, shown at the lower side (in the illustrated orientation) of  FIG. 2 , may be an electron conductor such as an n-type electron conductor. The n-type electron conductor may be transparent or at least substantially transparent to at least some wavelengths of light within the visible portion of the electromagnetic spectrum. 
         [0015]    In some cases, the n-type electron conductor may include or be formed so as to take the form of a structured pattern or array, such as a structured nano-materials or other structured pattern or array, as desired. The structured nanomaterials may include clusters or arrays of nanospheres, nanotubes, nanorods, nanowires, nano-inverse opals, or any other suitable nanomaterials or shapes as desired. The quantum dots are shown electrically coupled to or otherwise disposed on the electron conductor. In at least some embodiments, the quantum dots may be disposed over and “fill in” the structured pattern or array of the electron conductor, as shown in  FIG. 2 . 
         [0016]    It is contemplated that the electron conductor may be formed of any suitable material. In some cases, the electron conductor layer  16  may be an n-type electron conductor. In some instances, the electron conductor layer  16  may be metallic, such as TiO 2  or ZnO. In some cases, electron conductor layer  16  may be an electrically conducting polymer such as a polymer that has been doped to be electrically conductive or to improve its electrical conductivity. 
         [0017]    As described with respect to  FIG. 1 , solar cell  10  may include a bifunctional ligand layer  14 . In some cases, bifunctional ligand layer  14  may include a single bifunctional ligand or a large number of bifunctional ligands. A bifunctional ligand may, in some cases, be considered as improving electron transfer by reducing the energy barriers for electron transfer. A bifunctional ligand may provide a conduit so that electrons which are ejected by the quantum dots can travel to and through the electron conductor. A bifunctional ligand may, for example, secure the quantum dot relative to the electron conductor and/or any other related structure. 
         [0018]    A variety of bifunctional ligands may be used. In an illustrative but non-limiting example, a bifunctional ligand may be 2-[2-ethoxycarbonylmethylsulfanyl)ethyl]-1,3-thiazolidine-4-carboxylic acid, which has the structure: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0019]    Another illustrative but non-limiting example of a suitable bifunctional ligand is 2-acetylamino-3-benzylsulfanyl propanoic acid, which has the structure: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0020]    Another illustrative but non-limiting example of a suitable bifunctional ligand is isocysteine, which has the structure: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0021]    Another illustrative but non-limiting example of a suitable bifunctional ligand is 2-[(2-oxothiolan-3-yl)carbamoylmethylsulfanyl]acetic acid, which has the structure: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0022]    Another illustrative but non-limiting example of a suitable bifunctional ligand is phytic acid, which has the structure: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0023]    Another illustrative but non-limiting example of a suitable bifunctional ligand is pentetic acid, which has the structure: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0024]    As discussed with respect to  FIG. 1 , the illustrative solar cell  10  may include a hole conductor layer  18 . A variety of hole conductor materials are contemplated. For example, hole conductor layer  18  may be formed of a p-type electrically conductive polymer. In some instances, hole conductor layer  18  may be formed of or otherwise include: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    as a repeating unit, where n is an integer ranging from about 6 to about 12. In some cases, such a material may be formed via a Williamson ether synthesis process by combining an appropriate hydroxy-terminated alkyl thiophene with 5-chloromethyl-8-hydroxy quinoline in the presence of sodium hydride. 
         [0025]    Another illustrative but non-limiting example of a polymeric material suitable for forming hole conductor  18  may be formed by combining poly (3,6-hydroxyhexyl thiophene) with 5-chloromethyl-8-hydroxy quinoline in the presence of sodium hydride to provide the following structure as a repeating unit: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0026]    Another illustrative but non-limiting example of a polymeric material suitable for forming hole conductor  18  may be formed by combining poly(3,11-hydroxyundecyl thiophene) with 5-chloromethyl-8-hydroxy quinoline in the presence of sodium hydride to provide the following structure as a repeating unit: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0027]    Another illustrative but non-limiting example of a polymeric material suitable for forming hole conductor  18  may be formed by combining poly(3,12-hydroxydodecyl thiophene) with 5-chloromethyl-8-hydroxy quinoline in the presence of sodium hydride to provide the following structure as a repeating unit: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0028]    A particular example solar cell may have the following structure: an electron conductor including TiO2; a bifunctional ligand including 2-[2-(ethoxycarbonylmethylsulfanyl)ethyl]-1,3-thiazolidine-4-carboxylic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,6-hydroxyhexyl thiophene) functionalized with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0029]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including 2-acetylamino-3-benzylsulfanyl-propanoic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,6-hydroxyhexyl thiophene) functionalized with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0030]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including isocysteine; CdSe and/or other quantum dots; and a hole conductor including poly (3,6-hydroxyhexyl thiophene) functionalized with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0031]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including 2-[(2-oxothiolan-3-yl)carbamoylmethylsulfanyl]acetic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,6-hydroxyhexyl thiophene) functionalized with 5 chloromethyl-8-hydroxylquinoline as pendant group. 
         [0032]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including phytic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,6-hydroxyhexyl thiophene) functionalized with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0033]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including pentetic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,6-hydroxyhexyl thiophene) functionalized with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0034]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including 2-[2-(ethoxycarbonylmethylsulfanyl)ethyl]-1,3-thiazolidine-4-carboxylic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,11-hydroxyundecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0035]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including 2-acetylamino-3 benzylsulfanyl-propanoic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,11-hydroxyundecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0036]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including isocysteine; CdSe and/or other quantum dots; and a hole conductor including poly (3,11-hydroxyundecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0037]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including 2-[(2-oxothiolan-3-yl)carbamoylmethylsulfanyl]acetic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,11-hydroxyundecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0038]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including phytic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,11-hydroxyundecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0039]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including pentetic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,11-hydroxyundecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0040]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including 2-[2-(ethoxycarbonylmethylsulfanyl)ethyl]-1,3-thiazolidine-4-carboxylic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,12-hydroxydodecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0041]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including 2-acetylamino-3 benzylsulfanyl-propanoic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,12-hydroxydodecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline, as pendant group. 
         [0042]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including isocysteine; CdSe and/or other quantum dots; and a hole conductor including poly (3,12-hydroxydodecyl thiophene) with 5-chloromethyl-8 hydroxyquinoline, as pendant group. 
         [0043]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including 2-[(2-oxothiolan-3-yl)carbamoylmethylsulfanyl]acetic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,12-hydroxydodecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline, as pendant group. 
         [0044]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including phytic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,12-hydroxydodecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline as pendant group. 
         [0045]    Another particular example solar cell may have the following structure: an electron conductor including TiO 2 ; a bifunctional ligand including pentetic acid; CdSe and/or other quantum dots; and a hole conductor including poly (3,12-hydroxydodecyl thiophene) with 5-chloromethyl-8-hydroxyquinoline as pendant group. These are merely examples and are not intended to be limiting in any way. 
         [0046]    The disclosure should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the invention can be applicable will be readily apparent to those of skill in the art upon review of the instant specification.