Spectroelectrochemical Measurement of Surface Electrostatic Contributions to Colloidal CdSe Nanocrystal Redox Potentials

Understanding and controlling the redox properties of colloidal semiconductor nanocrystals is critical for application of this class of materials in many proposed technologies. Here, we use spectroelectrochemical potentiometry to analyze the redox potentials of free-standing colloidal n -type CdSe nanocrystals. We show that both the redox potentials and the maximum number of conduction-band electrons that can be accumulated through photodoping are strongly affected by the nanocrystal’s surface stoichiometry, varying reproducibly by over 400 meV with changes in relative Cd 2+:Se 2– surface concentration. The data suggest that Se 2– enrichment generates electric dipoles at the nanocrystal surfaces that shift the CdSe nanocrystal band-edge potentials to more negative values, and these generated dipoles are largely eliminated upon Cd 2+ binding. These results demonstrate the importance of nanocrystal surface stoichiometry in applications involving tuned nanocrystal redox potentials, band-edge alignment, or electron-transfer driving forces.