Spectroelectrochemistry of CdSe/CdS Core–Shell Quantum Dots

Understanding the effect of excess charges either in the excited state or in trap states in semiconductor nanocrystals is vital for optimizing their luminescence efficiency. Here, we report the effects of electrochemically injected holes and electrons on the optical properties of CdSe/CdS with varying shell thicknesses (0–8 monolayers). Electron injection leads to quasi-reversible changes to the optical properties of QDs, and the reversibility improves with increasing shell thickness. In contrast, hole injection induces lattice corrosion in bare CdSe QDs. However, the presence of CdS shells obviates decomposition and leads instead to carrier trapping and trion formation. We demonstrate that the behavior and relaxation dynamics of trions in colloidal CdSe/CdS quantum dots can be resolved as a function of the shell thickness using a combination of time-resolved photoluminescence spectroscopy and spectroelectrochemistry.