  Fulfilling the potential of the colloidal semiconductor quantum dots (QDs) in
electrically driven applications remains a challenge largely since operation of
such devices involves charged QDs with drastically different photo-physical
properties compared to their well-studied neutral counterparts. In this work,
the full picture of excited state dynamics in charged CdSe QDs at various
time-scales has been revealed via transient absorption spectroscopy combined
with electrochemistry as direct manipulation tool to control the negative
charging of CdSe QDs. In trions, excited states of single charged QDs, the
additional electron in the conduction band speeds up the hot electron cooling
by enhanced electron-electron scattering followed by charge redistribution and
polaron formation in picoseconds timescale. The trions are finally decayed by
Auger process in 500 ps timescale. Double charging in QDs, on the other hand,
decelerates the polaron formation process while accelerates the following Auger
decay. Our work demonstrates the potential of photo-electrochemistry as a
platform for ultrafast spectroscopy of charged species and paves a way for
further studies to develop comprehensive knowledge of the photophysical
processes in charged QDs more than the well-known Auger decay preparing their
use in future optoelectronic applications.
