Year: 2024
Type: article
Abstract: Using cyclic voltammetry under illumination, we recently demonstrated that CdS quantum dots (QDs) form charge donor states that live for at least several minutes after illumination ends, ∼12 orders of magnitude longer than expected for free carriers. This time scale suggests that the conventionally accepted mechanism of charge transfer, wherein charges directly transfer to an acceptor following exciton dissociation, cannot be complete. Because of these long time scales, this unconventional pathway is not readily observed using time-resolved spectroscopy to probe charge transfer dynamics. Here, we investigated the chemical nature of these charge donor states using cyclic voltammetry under illumination coupled with NMR spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and optical spectroscopy. Our data reveal that charges are stored locally rather than as free carriers, and the number of charges stored is dependent on the QD surface ligation and stoichiometry. Altogether, our results confirm that electrons are stored at ligated surface Cd, these sites are competent charge donors, and this storage is charge balanced by X-type ligand desorption. We found that charge storage occurs in every QD system studied, including CdS, CdSe, and InP capped with carboxylate and phosphonate ligands.
Source: ACS Nano
Institutions: University of Washington, University of Arizona
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
Awards: G1301677854, G1739289980, G199017485, G311062248, G3499273409, G4285111415, G4515799968, G5412571837, MRSEC: UW Molecular Engineering Materials Center, G6139170584, NNCI: Northwest Nanotechnology Infrastructure (NWNI), METAL-TIPPED AND ELECTROCHEMICALLY WIRED SEMICONDUCTOR NANOCRYSTALS: MODULAR CONSTRUCTS FOR DIRECTED CHARGE TRANSFER, G8862470763, MRSEC: UW Molecular Engineering Materials Center, G8880399141
OpenAlex ID: W4401715720