Boron nitride carbon alloy solar cells

Abstract

Solar cells fabricated from p-n junctions of boron nitride nanotubes alloyed with carbon are described. Band gaps of boron nitride carbon alloys are tailored by controlling carbon content in the boron nitride nanotubes. High efficiency solar cells can be fabricated by tailoring the band gap of boron nitride carbon alloy nanotubes, and using these nanotubes for fabricating solar cells u. Because boron nitride carbon alloy nanotubes are transparent to most wavelengths of light, the wavelengths not converted to electrons (i.e., absorbed) at a first p-n junction in a solar cell will pass through the stack to another p-n junction in the stack having a different band gap. At each successive p-n junction, each of which has a different band gap from the other p-n junctions in the stack, more wavelengths of light will be converted into electricity. This dramatically increases the efficiency of solar cells.

1 - 20 . (canceled) 
     
     
         21 . A solar cell having at least three layers, the solar cell comprising:
 a first layer of boron nitride carbon alloy nanotubes having a first carbon concentration;   a second layer of boron nitride carbon alloy nanotubes having a second carbon concentration greater than the first; and   a third layer of boron nitride carbon alloy nanotubes having a third carbon concentration greater than the second, wherein each of the layers exhibits a band gap different than that of the other layers.   
     
     
         22 . The solar cell of  claim 21  wherein each of the at least three layers has a density of less than 2 g/cc. 
     
     
         23 . The solar cell of  claim 21  wherein each layer comprises nanotube felts. 
     
     
         24 . The solar cell of  claim 21  wherein each layer comprises nanotubes oriented perpendicular to a plane of the layers. 
     
     
         25 . The solar cell of  claim 21  wherein each layer comprises nanotubes oriented horizontally to a plane of the layers. 
     
     
         26 . The solar cell of  claim 21  wherein one of the layers has a first wavelength of light for which it is most efficient at converting to electricity and at least one of the remaining layers is substantially transparent to that first wavelength. 
     
     
         27 . The solar cell of  claim 21  wherein each of the at least three layers transmits more than 50% of incident light. 
     
     
         28 . The solar cell of  claim 21  wherein each of the at least three layers exhibits a band gap of 0.7 eV to 2 eV. 
     
     
         29 . The solar cell of  claim 21  wherein the carbon atoms reside at a lattice site and not at an interstitial site or defect.