Light conversion efficiency enhanced solar cell fabricated with downshifting nanomaterial

Abstract

The light conversion efficiency of a solar cell ( 10 ) is enhanced by using an optical downshifting layer ( 30 ) in cooperation with a photovoltaic material ( 22 ). The optical downshifting layer converts photons ( 50 ) having wavelengths in a supplemental light absorption spectrum into photons ( 52 ) having a wavelength in the primary light absorption spectrum of the photovoltaic material. The cost effectiveness and efficiency of solar cells platforms ( 20 ) can be increased by relaxing the range of the primary light absorption spectrum of the photovoltaic material. The optical downshifting layer can be applied as a low cost solution processed film composed of highly absorbing and emissive quantum dot heterostructure nanomaterial embedded in an inert matrix to improve the short wavelength response of the photovoltaic material. The enhanced efficiency provided by the optical downshifting layer permits advantageous modifications to the solar cell platform that enhances its efficiency as well.

1 .- 27 . (canceled) 
     
     
         28 . An optical downshifting material, comprising:
 a liquid or matrix medium; and   a plurality of encapsulated quantum dot heterostructures (QDHs) disposed in the liquid or matrix medium, each QDH comprising:
 a nanocrystalline core comprising a first semiconductor material; 
 a nanocrystalline shell comprising a second, different, semiconductor material at least partially surrounding the nanocrystalline core; and 
 an encapsulating coating surrounding the nanocrystalline core and nanocrystalline shell pairing. 
   
     
     
         29 . The optical downshifting material of  claim 28 , wherein the material has an onset absorption wavelength approximately in the range of 500-600 nm. 
     
     
         30 . The optical downshifting material of  claim 29 , wherein the material has a light emission wavelength greater than approximately 600 nm. 
     
     
         31 . The optical downshifting material of  claim 30 , wherein the material has a maximum absorption wavelength of approximately 480 nm, and has a maximum emission wavelength of approximately 620 nm. 
     
     
         32 . The optical downshifting material of  claim 28 , wherein the medium is a matrix medium configured for application to a receiving surface in the form of a film. 
     
     
         33 . The optical downshifting material of  claim 32 , wherein the matrix is an inert polymer material matrix. 
     
     
         34 . The optical downshifting material of  claim 28 , wherein the medium is a liquid medium configured for application to a receiving surface in the form of a solution. 
     
     
         35 . The optical downshifting material of  claim 28 , wherein the encapsulating coating passivates the nanocrystalline core and nanocrystalline shell pairing of each QDH. 
     
     
         36 . The optical downshifting material of  claim 28 , wherein the encapsulating coating protects the nanocrystalline core and nanocrystalline shell pairing of each QDH from the liquid or matrix medium. 
     
     
         37 . The optical downshifting material of  claim 28 , wherein the encapsulating coating of each QDH is a silica coating. 
     
     
         38 . The optical downshifting material of  claim 28 , wherein the encapsulating coating of each QDH has a radius approximately in the range of 1-50 nm. 
     
     
         39 . The optical downshifting material of  claim 28 , wherein the first semiconductor material of each QDH is selected from the group consisting of zinc sulfide (ZnS) and cadmium sulfide (CdS). 
     
     
         40 . The optical downshifting material of  claim 28 , wherein the first semiconductor material of each QDH is cadmium selenide (CdSe) and the second semiconductor material is cadmium sulfide (CdS). 
     
     
         41 . The optical downshifting material of  claim 40 , wherein the CdSe nanocrystalline core of each QDH has no dimension greater than approximately 6 nm, and the CdS nanocrystalline shell has at least one dimension greater than approximately 15 nm and a second dimension approximately 1-2 nm thicker than a dimension of the CdSe nanocrystalline core. 
     
     
         42 . A method of fabricating an optical downshifting material, the method comprising:
 forming a plurality of encapsulated quantum dot heterostructures (QDHs), each QDH comprising:
 a nanocrystalline core comprising a first semiconductor material; 
 a nanocrystalline shell comprising a second, different, semiconductor material at least partially surrounding the nanocrystalline core; and 
 an encapsulating coating surrounding the nanocrystalline core and nanocrystalline shell pairing; and 
   suspending the plurality of QDHs in a liquid or matrix medium.   
     
     
         43 . The method of  claim 42 , wherein each QDH is formed by first forming a micelle around each nanocrystalline core and shell pairing and then growing the encapsulating coating inside of the micelle. 
     
     
         44 . The method of  claim 42 , wherein the medium is a matrix medium, the method further comprising:
 applying, in the form of a film, the matrix medium having the plurality of QDHs suspended therein to a receiving surface of a device.   
     
     
         45 . The method of  claim 42 , wherein the medium is a liquid medium, the method further comprising:
 applying, in the form of a solution, the liquid medium having the plurality of QDHs suspended therein to a receiving surface of a device.   
     
     
         46 . The method of  claim 42 , wherein suspending the plurality of QDHs in the liquid or matrix medium comprises protecting, by the encapsulating coating, the nanocrystalline core and nanocrystalline shell pairing of each QDH from the liquid or matrix medium. 
     
     
         47 . The method of  claim 42 , wherein forming each of the plurality of encapsulated QDHs comprises forming a cadmium selenide (CdSe) nanocrystalline core, forming a cadmium sulfide (CdS) nanocrystalline shell at least partially surrounding the CdSe nanocrystalline core, and forming a silica coating surrounding the CdSe nanocrystalline core and CdS nanocrystalline shell pairing.