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Download fileHole Cooling Is Much Faster than Electron Cooling in PbSe Quantum Dots
journal contribution
posted on 26.01.2016, 00:00 authored by Frank
C. M. Spoor, Lucas T. Kunneman, Wiel H. Evers, Nicolas Renaud, Ferdinand
C. Grozema, Arjan J. Houtepen, Laurens D. A. SiebbelesIn semiconductor quantum dots (QDs),
charge carrier cooling is
in direct competition with processes such as carrier multiplication
or hot charge extraction that may improve the light conversion efficiency
of photovoltaic devices. Understanding charge carrier cooling is therefore
of great interest. We investigate high-energy optical transitions
in PbSe QDs using hyperspectral transient absorption spectroscopy.
We observe bleaching of optical transitions involving higher valence
and conduction bands upon band edge excitation. The kinetics of rise
of the bleach of these transitions after a pump laser pulse allow
us to monitor, for the first time, cooling of hot electrons and hot
holes separately. Our results show that holes cool significantly faster
than electrons in PbSe QDs. This is in contrast to the common assumption
that electrons and holes behave similarly in Pb chalcogenide QDs and
has important implications for the utilization of hot charge carriers
in photovoltaic devices.