Quantum Dot Solar Cells: High Efficiency through Multiple Exciton Generation

Research output: Contribution to conferencePaper


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-holepairs 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 atabout 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.
Original languageAmerican English
Number of pages5
StatePublished - 2005
Event2004 DOE Solar Energy Technologies Program Review Meeting - Denver, Colorado
Duration: 25 Oct 200428 Oct 2004


Conference2004 DOE Solar Energy Technologies Program Review Meeting
CityDenver, Colorado

Bibliographical note

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)

NREL Publication Number

  • NREL/CP-590-37036


  • bandgap
  • impact ionization
  • multiple exciton generation (MEG)
  • photons
  • PV
  • quantum dots (QD)
  • semiconductor nanoparticles
  • thermodynamic conversion


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