Quantum Dot Solar Cells: High Efficiency through Multiple Exciton Generation

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Impact ionization is a process in which absorbed photons in semiconductors that are at least twice the bandgap can produce multiple electron-hole pairs. For single-bandgap photovoltaic devices, this effect produces greatly enhanced theoretical thermodynamic conversion efficiencies that range from 45-85%, depending upon solar concentration, the cell temperature, and the number of electron-hole pairs produced per photon. For quantum dots (QDs), electron-hole pairs exist as excitons. We have observed astoundingly efficient multiple exciton generation (MEG) in QDs of PbSe (bulk Eg = 0.28 eV), ranging in diameter from 3.9 to 5.7nm (Eg = 0.73, 0.82, and 0.91 eV, respectively). The effective ... continued below

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Hanna, M. C.; Ellingson, R. J.; Beard, M.; Yu, P.; Micic, O. I.; Nozik, A. J. et al. January 1, 2005.

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Impact ionization is a process in which absorbed photons in semiconductors that are at least twice the bandgap can produce multiple electron-hole pairs. For single-bandgap photovoltaic devices, this effect produces greatly enhanced theoretical thermodynamic conversion efficiencies that range from 45-85%, depending upon solar concentration, the cell temperature, and the number of electron-hole pairs produced per photon. For quantum dots (QDs), electron-hole pairs exist as excitons. We have observed astoundingly efficient multiple exciton generation (MEG) in QDs of PbSe (bulk Eg = 0.28 eV), ranging in diameter from 3.9 to 5.7nm (Eg = 0.73, 0.82, and 0.91 eV, respectively). The effective masses of electron and holes are about equal in PbSe, and the onset for efficient MEG occurs at about three times the QD HOMO-LUMO transition (its ''bandgap''). The quantum yield rises quickly after the onset and reaches 300% at 4 x Eg (3.64 eV) for the smallest QD; this means that every QD in the sample produces three electron-hole pairs/photon.

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5 p.

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  • Related Information: Presented at the 2004 DOE Solar Energy Technologies Program Review Meeting, 25-28 October 2004, Denver, Colorado. Also included in the proceedings available on CD-ROM (DOE/GO-102005-2067; NREL/CD-520-37140)

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  • Report No.: NREL/CP-590-37036
  • Grant Number: AC36-99-GO10337
  • Office of Scientific & Technical Information Report Number: 860690
  • Archival Resource Key: ark:/67531/metadc781202

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  • January 1, 2005

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  • Dec. 3, 2015, 9:30 a.m.

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  • April 6, 2017, 12:45 p.m.

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Hanna, M. C.; Ellingson, R. J.; Beard, M.; Yu, P.; Micic, O. I.; Nozik, A. J. et al. Quantum Dot Solar Cells: High Efficiency through Multiple Exciton Generation, article, January 1, 2005; Golden, Colorado. (digital.library.unt.edu/ark:/67531/metadc781202/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.