Web Release Date: March 30,
Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum Dots
and
Center for Basic Sciences, National Renewable Energy Laborarory, Golden, Colorado 80401, Department of Chemistry, University of Colorado, Boulder, Colorado 80309, and Naval Research Laboratory, Washington, D.C. 20375
Received February 10, 2005
Revised March 19, 2005
Abstract:
We report ultra-efficient multiple exciton generation (MEG) for single photon absorption in colloidal PbSe and PbS quantum dots (QDs). We employ transient absorption spectroscopy and present measurement data acquired for both intraband as well as interband probe energies. Quantum yields of 300% indicate the creation, on average, of three excitons per absorbed photon for PbSe QDs at photon energies that are four times the QD energy gap. Results indicate that the threshold photon energy for MEG in QDs is twice the lowest exciton absorption energy. We find that the biexciton effect, which shifts the transition energy for absorption of a second photon, influences the early time transient absorption data and may contribute to a modulation observed when probing near the lowest interband transition. We present experimental and theoretical values of the size-dependent interband transition energies for PbSe QDs. We present experimental and theoretical values of the size-dependent interband transition energies for PbSe QDs, and we also introduce a new model for MEG based on the coherent superposition of multiple excitonic states.
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