Ultrafast Spectroelectrochemistry Reveals Photoinduced Carrier Dynamics in Positively Charged CdSe Nanocrystals

Extra charges in semiconductor nanocrystals are of paramount importance for their electrically driven optoelectronic and photovoltaic applications. Optical excitations such charged lead to rapid recombination via an Auger process, which can deteriorate the performance corresponding devices. While numerous articles report trion processes negatively nanocrystals, optical studies well-controlled positive charging detailed trions remain rare. In this work, we used electrochemistry achieve CdSe so-called quantum dots (QDs), a controlled way. Femtosecond transient absorption spectroscopy was applied situ investigation charge carrier dynamics after excitation electrochemically QD assembly on TiO2. We observe that without bias (i.e., neutral QDs), sub-picosecond hot cooling is followed by multiple phases electron injection transfer Positive first leads activation hole traps close valence band maximum, opens channel excitation. A further increase interrupts TiO2, if positively charged, it relaxation few hundred picosecond timescale. This study represents step toward understanding effect under conditions closely mimic potential