Multiple Exciton Dissociation in CdSe Quantum Dots by Ultrafast Electron Transfer to Adsorbed Methylene Blue

摘要

Multiexciton generation in quantum dots (QDs) may provide a new approach for improving thensolar-to-electric power conversion efficiency in QD-based solar cells. However, it remains unclear how tonextract these excitons before the ultrafast exciton-exciton annihilation process. In this study we investigatenmultiexciton dissociation dynamics in CdSe QDs adsorbed with methylene blue (MB+) molecules by transientnabsorption spectroscopy. We show that excitons in QDs dissociate by ultrafast electron transfer to MB+nwith an average time constant of ∼2 ps. The charge separated state is long-lived (>1 ns), and the chargenrecombination rate increases with the number of dissociated excitons. Up to three MB+ molecules per QDncan be reduced by exciton dissociation. Our result demonstrates that ultrafast interfacial charge separationncan effectively compete with exciton-exciton annihilation, providing a viable approach for utilizing shortlivednmultiple excitons in QDs.