Abstract
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 language | American English |
|---|---|
| Number of pages | 5 |
| State | Published - 2005 |
| Event | 2004 DOE Solar Energy Technologies Program Review Meeting - Denver, Colorado Duration: 25 Oct 2004 → 28 Oct 2004 |
Conference
| Conference | 2004 DOE Solar Energy Technologies Program Review Meeting |
|---|---|
| City | Denver, Colorado |
| Period | 25/10/04 → 28/10/04 |
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
Keywords
- bandgap
- impact ionization
- multiple exciton generation (MEG)
- photons
- PV
- quantum dots (QD)
- semiconductor nanoparticles
- thermodynamic conversion
