Hybrid Photovoltaic Cells and Related Methods

Abstract

Embodiments of the present invention involve photovoltaic (PV) cells comprising a semiconducting nanorod-nanocrystal-polymer hybrid layer, as well as methods for fabricating the same. In PV cells according to this invention, the nanocrystals may serve both as the light-absorbing material and as the heterojunctions at which excited electron-hole pairs split.

1 . A photovoltaic cell comprising:
 a. first and second electrodes;   b. a plurality of aligned semiconducting nanorods disposed between the electrodes, each nanorod being electrically connected to the first electrode and electrically insulated from the second;   c. a plurality of photoresponsive nanocrystals surrounding and bound to the nanorods; and   d. a semiconductor polymer surrounding the nanorods and bound to the nanocrystals and to at least the second electrode, whereby the nanocrystals act as heterojunctions channeling a first charge carrier into the nanorods and a second charge carrier into the polymer.   
     
     
         2 . The cell of  claim 1  wherein (i) the polymer is a hole-transfer polymer, (ii) the first charge carrier is electrons, and (iii) the second charge carrier is holes. 
     
     
         3 . The cell of  claim 2  wherein the polymer is poly(3-hexylthiophene), polyphenylenevinylene or a derivative thereof, or polyfluorene or a derivative thereof. 
     
     
         4 . The cell of  claim 1  wherein the nanorods are wide-bandgap semiconductors. 
     
     
         5 . The cell of  claim 4  wherein the nanorods comprise at least one of ZnO, SnO, and/or TiO 2 . 
     
     
         6 . The cell of  claim 1  wherein the nanorods are single-crystal nanorods. 
     
     
         7 . The cell of  claim 1  wherein the nanorods have an aspect ratio of at least 3. 
     
     
         8 . The cell of  claim 1  wherein the nanorods are bound to the nanocrystal by a bifunctional capping agent. 
     
     
         9 . The cell of  claim 8  wherein the capping agent is mercaptoacetic acid. 
     
     
         10 . The cell of  claim 1  wherein absorption of light by a nanocrystal results in production of an exciton, the nanocrystal having a largest spatial dimension no greater than an average diffusion distance of the exciton. 
     
     
         11 . The cell of  claim 1  wherein the nanocrystals comprise at least one of CuInSe 2 , CuInS 2 , CuIn 1−x Ga x Se 2 , GaAs, InAs, InP, PbS, PbSe, PbTe, GaSb, InSb, CdTe and CdSe, wherein 0≦x≦1. 
     
     
         12 . The cell of  claim 1  wherein the nanocrystals have extinction coefficients of at least 100,000 M −1 cm −1 . 
     
     
         13 . The cell of  claim 1  wherein the semiconductor polymer is bound to the nanocrystals but not to the nanorods. 
     
     
         14 . A method of fabricating a semiconductor structure comprising heterojunctions and being suitable for use in a photovoltaic cell, the method comprising the steps of:
 a. providing a plurality of nanorods and a plurality of photoresponsive nanocrystals capped with a first capping agent;   b. exposing the nanorods or the nanocrystals to a second, bifunctional capping agent;   c. thereafter combining the nanocrystals with the nanorods, whereby the nanocrystals bind to the nanorods via the bifunctional capping agent;   d. combining the bound nanorods and nanocrystals with a functionalized monomer having a binding group, the binding group (i) exhibiting a stronger affinity for the nanocrystals than the first capping agent and (ii) exhibiting a weaker affinity for the nanorods than the bifunctional capping agent, whereby the monomer preferentially displaces the first capping agent so as to bind to the nanocrystals but not to the nanorods; and   e. polymerizing the monomer.   
     
     
         15 . The method of  claim 14  further comprising the step of disposing the nanorods between the first and second electrodes, the nanorods each having one end in electrical contact with the first electrode, and being electrically insulated from the second electrode through a thin polymer layer at the other end. 
     
     
         16 . The method of  claim 14  further comprising, before step (a), the step of growing a plurality of nanorods on a substrate providing the first electrode. 
     
     
         17 . The method of  claim 16  further comprising, after step (e), the step of depositing the second electrode, the second electrode being electrically insulated from the nanorods through a thin polymer layer. 
     
     
         18 . The method of  claim 14  wherein step (a) involves providing a nanocrystal capped with a first capping agent containing at least one binding functionality selected from the group consisting of thiol, selenol, amine, phosphine, phosphine oxide, or an aromatic heterocycle. 
     
     
         19 . The method of  claim 18  wherein the first capping agent is octanethiol. 
     
     
         20 . The method of  claim 14  wherein step (b) comprises capping the nanorods with the second capping agent, the first capping agent having a weaker affinity for the nanocrystals than the second capping agent, whereby the second capping agent preferentially displaces the first capping agent so as to bind to the nanocrystal. 
     
     
         21 . The method of  claim 14  wherein step (b) comprises exposing the nanocrystals to the second capping agent, the second capping agent replacing some but not all of the first capping agent on the nanocrystals, whereby in step (c) the free ends of the second capping agent bind to the nanorods.