Excited-State Electron Transfer in Quantum Dot Heterostructures
David F. Watson
Department of Chemistry, University at Buffalo, The State University of New York
Buffalo, New York 14260-3000
Semiconductor quantum dots (QDs) are intriguing light-harvesters and excited-state charge donors for solar energy conversion, due to their size-dependent optical properties and band-edge potentials, high oscillator strengths, and the possibilities of hot-carrier extraction and multiexciton generation. Integration of colloidal QDs into heterostructures may afford programmable interfacial energetic offsets and tunable interfacial distance, electronic coupling, and excited-state charge-transfer reactivity. Such architectures are intriguing for fundamental studies and as candidates to harvest light and concentrate charges for solar energy conversion.
This presentation will focus on our recent research pertaining to two types of QD heterostructures. The first is prepared by tethering colloidal QDs to each other via the formation of amide bonds between terminal functional groups of the capping ligands. Several formulations of heterostructures, with varying compositions and interfacial energetic offsets, have been prepared via this approach. Time-resolved absorption and emission measurements have revealed that photoexcitation of QDs within such heterostructures can lead to rapid excited-state electron or hole transfer and long-lived charge separation.
The second type of heterostructure consists of cadmium chalcogenide QDs interfaced with metal-intercalated vanadium pentoxide nanowires (NWs). Intercalative mid-gap states of the NWs overlap in energy with valence-band states of the QDs, facilitating the transfer of holes, on picosecond time scales, from photoexcited QDs to the NWs. Such heterostructures are interesting candidates for photocatalyst platforms.
Recent results pertaining to the synthesis and characterization of various heterostructures, as well as the spectroscopic characterization of excited-state charge transfer, will be highlighted in this presentation.