The electronic structure of PbS colloidal quantum dot (CQD) solids is discussed with a focus on the states principally involved in charge transport and the influence ligands have on these states.  The mechanism of charge transport in CQD solids has, until now, been controversial. Using ultrafast vibrational spectroscopy in partnership with leaders in the CQD photovoltaic field, we demonstrate the existence of electron transport states that lie at the Stokes shift energy below optically allowed band states in CQD solids.  Electrons do not need to be promoted to optically allowed quantum confined states to undergo efficient charge transport.  Instead, electrons in these Stokes shifted transport states exhibit activated charge transport with activation energies of order 50 meV due to a combination of shallow trap states and energetic disorder arising from polydispersity of the CQDs in the solids.

Stokes shifted electron transport states in quantum dot solids

246th National Meeting (2013)

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