In Situ Studies of Multi-Carrier Dynamics in Electrochemically-Charged Colloidal CdSe/CdS Core/Shell Quantum Dots

The application of semiconductor nanocrystals (NCs) in optoelectronic devices and photocatalysis inevitably involves them in charged states. The carrier and exciton dynamics of electrochemically charged NCs in solutions have yet to be reported. Herein, the electrochemical charging effects in colloidal CdSe/CdS core/shell quantum dots (QDs) are systematically investigated using static spectroelectrochemistry (SEC) and in situ transient absorption (TA) spectroscopy. Static SEC reveals the presence of in-gap trap states from 0.9 eV below the conduction band (CB) edge. Negligible changes in TA spectra and kinetics were observed from open circuit potential (OCP) to more anodic potentials within the QD band gap. At cathodic potentials, the negatively charged QDs show band edge trion decay with a lifetime of 690 ± 31 ps and slower 1P to 1S electron relaxation with time constants of 12.4 ± 0.8 ps assigned to the spin blockade effect and 316 ± 35 ps assigned to the phonon bottleneck effect. Our study reveals rich effects of charging on QD excited state under nearly native conditions.