Photo-Excitation Dynamics in Electrochemically Charged CdSe Quantum Dots: from Hot Carrier Cooling to Auger Recombination of Negative Trions

Abstract: 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.