APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011;
Dallas, Texas
Abstract: P41.00001 : Excitons at Interfaces
8:00 AM–8:36 AM
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Solar photovoltaics based on molecular and nano materials
commonly involve excitons. This results from strong Coulomb
attraction between an electron and a hole due to the low
dielectric constants of molecules or quantum confinement of nano
materials. In this lecture, I will address the question of how
excitons dissociate at donor/acceptor interfaces. The first
example deals with charge separation in organic photovoltaics.
Due to the low dielectric constant of organic materials, an
electron-hole pair across an organic donor/acceptor interface is
bound by the Coulomb potential. This gives rise to a set of
H-atom like states called charge-transfer excitons, as observed
experimentally. The lowest energy charge transfer exciton state
has a binding energy much higher than kT at room temperature.
This leads to the conclusion that hot charge transfer exciton
states must be involved in charge separation in organic
photovoltaics. The second example deals with hot exciton
dissociation due to electron transfer from photo-excited
semiconductor nanocrystals (PbSe) to an electron acceptor (TiO2),
an issue of particular interest to hot carrier solar cells with
theoretical solar conversion efficiency surpassing the
Shockley-Queisser limit. We show that, with appropriate chemical
treatment of the nanocrystal surface, ultrafast transfer of a hot
electron can be competitive with hot exciton relaxation due to
phonon scattering. The last example will show recent development
on hot carrier scattering and multiple exciton generation (MEG)
in semiconductor nanorystals.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.P41.1